The Metaphysical Challenge of Solipsism

In this essay, I am going to demonstrate first, that the logical consequence of a pure Metaphysical Idealism is Metaphysical Solipsism.  But then I will argue that a rational Solipsist will behave as if she were a non-Solipsist.  In the final analysis, a rational Solipsist will find herself much better off if she actually dis-believes Solipsism, even if she actually believes Solipsism is true  -  a contradictory position that is one of the main arguments against its probable truth.  I will close the essay by pointing out three additional problems that a consistent Solipsist must deal with.  Solipsism, I suggest, is a self-consistent philosophy that does entail a number of consequences that most people find difficult to swallow.  For those reasons, Solipsism is not a seriously held position by any known philosopher.

Solipsism

Solipsism comes from the latin "Solus ipse"  - the sole self.  Anthony Flew defines solipsism as "The theory that I am the sole existent.  To be a solipsist I must hold that I alone exist independently, and that what I ordinarily call the outside world exists only as an object or content of my consciousness."(1)  Thomas Mautner defines it as "(1-metaphysics) the view that nothing exists except one's own self and the contents of its consciousness; (2-epistemology) the view that nothing can be known except one's own self and the contents of its consciousness."(2)

Clearly "in here" is distinct from "out there".  In here, I am me.  Out there is everything else that is not me.  The distinction is self-evident.  Solipsism is the belief that one's self is the only thing that exists.  It is the extreme form of empirical scepticism about our evidence of reality.  Solipsism is the doctrine that, in practice as well as principle, "evidence" means for me my experiences, "reality" means for me the world that I perceive, and "existence" means for me my existence.  In other words, everything which I experience  -  everything that is not-me (other people, events and processes, in short anything which would commonly be regarded as a constituent of the spatio-temporal matrix in which I exist)  -  just part of the content of my experiences, of my consciousness.  Other objects, including other beings that may appear to exist separately from me, are actually just projections of my own consciousness upon my experiences.  According to Solipsism, I see the world through the eyes of my mind.  The world is only as I perceive it.  Reality is only that which seems real to me.  Knowledge is what I know.  Egoism is the only possible ethic  -  my welfare the only possible concern.

The interesting feature of Solipsism is that there is no discernable difference between the Solipsist's experiences of the world, and the non-Solipsist's experiences of the world.  In both cases their respective experiences will be rich, complex, and varied.  Further, there is no fundamental reason for a difference in moral attitude between the Solipsist and the non-Solipsist.  The only difference is their respective metaphysical assumptions about the ultimate foundation of those sensory experiences.  The Solipsist maintains that there is only my experiences.  The non-Solipsist maintains that there is something extra beyond my experiences.  But the Solipsist can draw upon Ockham's Razor to argue that there is no discernable benefit to me, and no discernable difference to my current or future experiences, from positing anything in addition to the summation of my personal experiences.  Not only can the existence of an external reality not be proved, it is not even necessary to adequately explain all of my past, present, and future experiences.

The challenge that Solipsism raises for the study of Philosophy is that while it seems to be a logically sound theory of existence, no one likes the implication that they are completely alone in the Universe.  It is also universally (and frequently offensively) rejected by philosophers as an acceptable basis of metaphysics.  Yet given certain popular metaphysical premises, philosophers have difficulty in rationally supporting this rejection.  Hence the challenge that Solipsism presents.

Metaphysics

In the popular mind, the term "metaphysical" has come to signify any form of reasoning which is taken to be excessively general, abstract, and subtle.  But among philosophers, especially from Descartes onward, it has come to have the distinct sense of having to do with what lies beyond, under, or behind what is available to the senses.  Hence, in modern Philosophy, "Metaphysics" is that branch of philosophical inquiry that involves a critical analysis of our most fundamental beliefs about the meaning and nature of "reality".  It is an inquiry into the nature of things based on logical reasoning rather than empirical methods.  Metaphysics progresses by identifying and then critically examining the logical consequences of our most fundamental beliefs about the world.  Unlike scientific investigation, the methods of metaphysics do not rely on the evidence.  Instead, the question of just what evidence is, and how to interpret what the evidence means, is a central issue of discussion.  And unlike religion, if the logical consequences should turn against the initial presumptions, it is not acceptable to redefine the rules so that they support the presumption.  THe study of metaphysics follows through on the logical consequences to see whatever might result.

In theory at least, the approach of metaphysics is to question everything.  Nothing is supposed to be immune to its searching examination for the logical consequences of our most fundamental beliefs.  Yet like all human endeavours, metaphysics is a human occupation.  And human minds need a place to start, a place to stand from which to move the world.  So in practice, the study of metaphysics is done by philosophers who critically examine each others beliefs.  Because it is so difficult to criticise one's own fundamental beliefs, only very rarely do you find one who willingly critically examines his own beliefs.  The study of Metaphysics, in practice therefore, progresses through the give and take of opposing views on various topics.  And a prime example is the question of the relationship between the Self and the World.  Just what is "me/myself/I"?  Just what is "reality"?  What (if any) uniqueness does each of these possess?

The "Inside-Out" Tradition

In the history of Metaphysics, there are two quite distinct traditions about the nature of the relationship between our self and the world we see around us  -  between what we think we perceive and what believe is real; and centrally, between the meaning of "perceive" and the meaning of "real".  They are the Idealist, or the "Inside-Out" tradition and the Realist or "Outside-In" tradition. (First introduced in the chapter on The Nature of Reality.)  The difference between the two traditions is the difference in their approach.  The Outside-In tradition sets out what must in a very general way be the case about the world and about ourselves if the world exists independent of our consciousness of it.  The Inside-Out tradition holds that only things answering to certain criteria are real with the result that there are distinct realms to be called "appearance" and "reality" respectively. 

Philosophers of the Inside-Out tradition maintain that our modes of consciousness and cognition constitute, modify, or process what we perceive as sensory inputs.  What our consciousness is aware of as sensory evidence must be regarded as the products of our consciousness rather than unbiased evidence of reality.  In that event, goes the inescapable logical conclusion, either we can know nothing about the "True" nature of an alleged external reality, or anything that we can know about such an alleged external reality must be provided through other means than our senses.  The proponents of the "Inside-Out" line of reasoning assume that consciousness, as prior and primary to the sensory evidence, must generate our understanding from the evidence provided by our processes of perception.  Perception is a separate process from our conscious awareness of what we perceive.  Our understanding of what we perceive is not a pure product of our senses.  Therefore, what we understand about our perceptions cannot be trusted as evidence for a separate reality.  We have no independent basis from which to validate the evidence provided by our senses.  All we have is the evidence of our perceptions.  And our perceptions are highly processed information from our senses.

There is, therefore, no logically valid line of reasoning that can proceed from the basic axiom that consciousness is the fundamental given, to the conclusion that there is a reality outside of, or separate from one's own consciousness.  Since there is no way to validate the evidence of the senses (the senses being the only source of information), there is no basis from which to conclude that the sensory evidence is valid evidence of an external reality.  There is no way to distinguish between "reality" and a dream or hallucination.  Philosophers of the Inside-Out Tradition therefore almost universally conclude that all that is perceived (ie. all the evidence), as well as all the contents of consciousness, is actively a product of consciousness.  As it is impossible to logically derive the existence of a reality beyond our subjective experience, therefore there can be no knowledge of such an external objective reality.  Hence, there is no acceptable proof that there is such an external objective reality. 

The inescapable consequence of this conclusion is that there can be no possible logical foundation for any constraints on the nature of the contents of a particular person's consciousness.  There can be no logical foundation for any standardization or similarity of the contents of consciousness from one person to another.  For this reason, the Inside-Out tradition logically results in what is referred to as "Subjectivist" (or sometimes "Anti-Realist" ) notions of Truth, Knowledge, and Ethics.  And, ultimately, to metaphysical "Solipsism".

Historical Development of Solipsism

Before going into greater detail on the nature of Solipsism, it would be helpful to provide a precis of the historical development of Solipsism.  I will start with a word or two on "Empiricism".  Empiricism is the philosophical doctrine that all human knowledge comes ultimately from senses and experience.  Strict Empiricism denies that humans have innate ideas or that anything is knowable prior to any experience.  The empiricist stands in particular opposition to those philosophies that maintain that we have other means of obtaining such knowledge such as intuition, revelation, or innate knowledge.  Often, empiricism is particularly contrasted with "rationalism", a theory which holds that the mind may apprehend some truths directly, without requiring the medium of the senses.  Philosophers generally associated with empiricism include Aristotle (384-322 BC), St. Thomas Aquinas (1225-1274), Sir Francis Bacon (1561-1626), Thomas Hobbes (1588-1679), John Locke (1632-1704), Bishop George Berkeley (1685-1753), and David Hume (1711-1776).

Empiricism is generally regarded as being at the heart of the modern scientific method.  Empiricism presumes that our theories should be based on our observations of the world rather than on intuition or faith  -  that is, empirical research and a posteriori inductive reasoning.  "Empirical" is an adjective often used in conjunction with both the natural and social sciences.  In its use within the sciences, "empiricism" means the use of working hypotheses which are capable of being disproved using observation or experiment (ie: ultimately through experience).

Ever since Aristotle, it has been the Empiricist's thesis that our only source of information about the world is our sensory experiences.  My knowledge of the world consists of my judgements based on my sensory experiences.  But an empiricist of the Inside-Out Tradition faces a difficulty first discussed in detail by Rene Descartes. 

Rene Descartes (1596-1650) was a French mathematician, physicist and philosopher.  Among his many other accomplishments, his most famous philosophical work was Meditations on First Philosophy (1641).  Descartes began his philosophical career by trying to apply to philosophy the basic principles of the new scientific method that Galileo had introduced and which had proved so successful.  Thus, one of his main aims in the Meditations was to provide a sound basis for scientific methods.  He aimed to show that the real source of scientific knowledge lay in the mind and not in the senses.  (He was, therefore not an empiricist, but the first of the "Rationalists".)  In attempting to find this real source of knowledge, Descartes hit upon the idea of using doubt as a tool or a weapon against doubt itself:

"I ought to reject as downright false all opinions which I could not imagine to be in the least degree open to doubt-my purpose being to discover whether, after doing so, there might not remain, as still calling for belief, something entirely indubitable."  (Rene Descartes, Discourse on Method(3)

In order to show that science rested on firm foundations and that these foundations lay in the mind and not the senses, Descartes began by bringing into doubt all the beliefs that come to us from the senses.  His aim in these arguments is not really to prove that nothing exists or that it is impossible for us to know if anything exists, but to show that all our knowledge of these things through the senses is open to doubt.  The Cartesian thesis was that the "I" that is me is not my eyes, or my ears, etc.  What I am most directly in touch with is my mind and its contents.  My senses are outside of the me that is the "I" of my mind.  They provide me with data that I must interpret and understand.  But it is not a verifiable fact that I have eyes and ears with which to see and hear.  Beginning with Descartes, philosophers of the Inside-Out tradition have had to deal with the dichotomy between "reality" and "appearance".  As in the movie "The Matrix", I could be the literal or functional equivalent of a "brain in a vat".  All of what I take to be my sensory inputs might be mere "appearances" provided by something other than what I assume.  The only thing I can know with any confidence is that "I" am me.

If our scientific knowledge comes to us through the senses, we can not even be certain that anything outside of us exists.  The logical consequence is that, since we do seem to "know" that external objects exist, this knowledge cannot come to us through the senses, but only through the mind.  As Rene Descartes stated in the second meditation, the contents of his mind seemed to be directly available to him. 

"I am, however, a real thing, and really existent; but what thing?  The answer was, a thinking thing...since it is now manifest to me that bodies themselves are not properly perceived by the senses nor by the faculty of imagination, but by the intellect alone; and since they are not perceived because they are seen and touched, but only because they are understood [or rightly comprehended by thought], I readily discover that there is nothing more easily or clearly apprehended than my own mind"  (Rene Descartes, Meditations on the First Philosophy(4)

Descartes uses three very similar arguments to open all our empirical knowledge to doubt: The dream argument, the deceiving God argument, and the evil demon argument.  The basic idea in each of these is that we never perceive external objects directly, but only through the contents of our own mind  -  through the images the supposedly external objects produce in us.  This thesis has since become known as the "Cartesian Theatre" model of sensory perception.  Since sense experience never puts us in direct contact with the objects themselves, but only with mental images displayed in some "Cartesian Theatre", sense perception provides no certainty that there is anything in the external world that corresponds to the images we have in our mind.  What is displayed on the theatre screen in the Cartesian Theatre might just as easily come from other sources than the alleged external objects that they appear to come from.

The dream argument goes like this: I often experience perceptions very much like the ones I usually have while awake, but while I am dreaming.  There are no definite signs to distinguish dream experiences from waking experiences.  Therefore, it is possible that I am dreaming right now and that all of my perceptions are a product of my mind and not a reflection of an external reality.  The deceiving God argument goes like this: I believe that there is a God who has created me and who is all powerful.  He has it in his power to deceive me even about what I seem to see clearly.  Therefore, it is possible that I am deceived about the nature of the world.  To allay the criticisms of those who might object that an omni-benevolent God would not so systematically deceive us, his famous evil demon argument runs similarly: Assume that there exists an evil demon, who is capable of deceiving me even about what I seem to see clearly.  Therefore, I have reason to doubt what my senses tell me, as well as the mathematical knowledge that I seem to have.  It is therefore possible that all knowledge of external objects, including my body, could be the result of the actions of an evil demon, and thus not a reflection of an external reality. 

On the basis of these three arguments, Descartes reasons that he has no sure knowledge of anything outside of his mind.  By introducing "methodological doubt" into philosophy, Descartes created the backdrop against which Solipsism subsequently developed, and was made to seem, if not plausible, at least irrefutable.  He still has to make a crucial leap of faith to the existence of objects outside of his mind.  He must do this, however, strictly on the basis of the contents of his own mind.  It is the idea of God that he finds in his mind that allows him to make this leap, and which forms the basis for his knowledge of all other external objects.  Without this leap, without this extra unsupported assumption, Descartes methodological doubt would unavoidably result in pure metaphysical Solipsism.

Bishop George Berkeley (1685-1753) carried the scepticism of Descartes to the next logical level.  Berkeley was an Irish philosopher and clergyman of the Anglican Church.  He is generally regarded as the founder of the modern school of Metaphysical Idealism.  His philosophical arguments were published in A Treatise Concerning The Principles of Human Knowledge (1710) and The Three Dialogues Between Hylas and Philonous (1713).  In the first of the three Socratic dialogues in this latter work, Berkeley's Philonous neatly manoeuvres Hylas into admitting that all that he actually perceives are but ideas in his mind.  All of the characteristics that Hylas initially takes to be properties of "material things", Philonous argues are properties of ideas in the mind.  And all of what Hylas takes as perceptions of external objects, Philonous argues are but perceptions of ideas of mind.  Berkeley's philosophy can be summed up nicely withhis catch-phrase "To be is to be perceived".

"It is evident to any one who takes a survey of the objects of human knowledge, that they are either ideas actually imprinted on the senses, or else such as are perceived by attending to the passions and operations of the mind, or lastly ideas formed by help of memory and imagination, either compounding, dividing, or barely representing those originally perceived in the aforesaid ways."  (George Berkeley, A Treatise Concerning The Principles of Human Knowledge(5)

Berkeley attempts to eliminate the problematic chasm between our perceptions and the supposed objects that are the cause of those perceptions by claiming that there are no objects that are the cause of our perceptions.  Rather, our perceptions constitute the whole of reality in themselves.  And like Descartes, he saves his philosophical position from pure Solipsism by postulating that the things that he takes to be external to his own mind are in fact ideas in the mind of God.  So-called "material things" gain their apparently objective existence and persistence by being perceived by God.

David Hume, following in the steps of Berkeley, brought to the empirical scepticism of Descartes and Berkeley an atheist's refusal to permit the God escape clause.  Hume was a Scottish philosopher and historian who argued in the empiricist tradition that human knowledge arises only from sense experience.  His most philosophically significant works were A Treatise of Human Nature (1739-1740) and An Inquiry Concerning Human Understanding (1748).  Hume raised perplexing and troublesome doubts about many of the basic assumptions upon which the laws of logic and science are constructed.  As a result of following the Inside-Out tradition of assuming the primacy of consciousness, he finds himself firmly painted into the Solipsist's corner.

"Experience is a principle, which instructs me in the several conjunctions of objects for the past. Habit is another principle, which determines me to expect the same for the future; and both of them conspiring to operate upon the imagination, make me form certain ideas in a more intense and lively manner, than others, which are not attended with the same advantages. Without this quality, by which the mind enlivens some ideas beyond others (which seemingly is so trivial, and so little founded on reason) we cou'd never assent to any argument, nor carry our view beyond those few objects, which are present to our senses. Nay, even to these objects we cou'd never attribute any existence, but what was dependent on the senses; and must comprehend them entirely in that succession of perceptions, which constitutes our self or person. Nay farther, even with relation to that succession, we cou'd only admit of those perceptions, which are immediately present to our consciousness, nor cou'd those lively images, with which the memory presents us, be ever receiv'd as true pictures of past perceptions. The memory, senses, and understanding are, therefore, all of them founded on the imagination, or the vivacity of our ideas."   (David Hume, A Treatise of Human Nature(6) )

Hume clearly finds the logical consequence of his Inside-Out premises singularly dissatisfying.  His "escape clause" is at once more fanciful and more practical than his predecessors' policy of adopting the premise of God, if perhaps not properly philosophical.  He ignores the problem and goes off to play a game of backgammon:

"Most fortunately it happens, that since reason is incapable of dispelling these clouds, nature herself suffices to that purpose, and cures me of this philosophical melancholy and delirium, either by relaxing this bent of mind, or by some avocation, and lively impression of my senses, which obliterate all these chimeras. I dine, I play a game of backgammon, I converse, and am merry with my friends; and when after three or four hours' amusement, I wou'd return to these speculations, they appear so cold, and strain'd, and ridiculous, that I cannot find in my heart to enter into them any farther."  (David Hume, A Treatise of Human Nature(6) )

Immanuel Kant (1724-1804), following in Hume's footsteps, tried to dispel Hume's "clouds" by directing his thinking away from the empiricism of his predecessors.  Although Kant was undoubtedly a genius of the first order, and arguably the most pre-eminent philosopher of the Inside-Out (Idealist) Tradition, he constructed a comprehensive system of philosophy that ranks among the greatest intellectual stumbles in Western philosophy.  His classic works, Critique of Pure Reason (1781) and Critique of Practical Reason (1788), mark the beginning of a general turn of Western philosophy away from the empirical/scientific approach of Aristotle and Hume, and the beginning of the end of the "Age of Enlightenment" (circa 1650 - circa 1790).

Kant suggested that although the content of experience must be discovered through experience itself, the mind imposes form and order on all its experiences, and this form and order is innate knowledge that can be discovered by reflection alone.  Kant brought to Hume's empirical scepticism the recognition that our notions of space and time cannot be knowledge learned from experience, since they are a necessary a priori scaffolding to any understanding of our sensory experiences.  Thus, human beings are capable of viewing only the appearance and not things as they are in themselves.

"Now a thing in itself cannot be known through mere relations; and we may therefore conclude that since outer sense gives us nothing but mere relations, this sense can contain in its representation only the relation of an object to the subject, and not the inner properties of the object in itself.  This also holds true of inner sense, not only because the representations of the outer senses constitute the proper material with which we occupy our mind, but because the time in which we set these representations, which is itself antecedent to the consciousness of them in experience, and which underlies them as the formal condition of the mode in which we posit them in the mind, itself contains [only] relations of succession, coexistence, and of that which is coexistent with succession, the enduring."  (Immanuel Kant.  Critique of Pure Reason (7) )

Kant breaks with the Cartesian tradition when he describes the subject, the human being, as not having direct access to his own mind.  For Kant, both external objects and inner sense are presented as appearances to the subject.

"If the faculty of coming to consciousness of oneself is to seek out (to apprehend) that which lies in the mind, it must affect the mind, and only in this way can it give rise to an intuition of itself.  But the form of this intuition, which exists antecedently in the mind, determines, in the representation of time, the mode in which the manifold is together in the mind, since it then intuits itself not as it would represent itself if immediately self-active, but as it is affected by itself, and there as it appears to itself, not as it is."  (Immanuel Kant.  Critique of Pure Reason (8) )

Thus, the mind, as a thing in itself, is not directly available to the understanding.  If any direct knowledge of one's own mind is unavailable, it hardly seems possible to know whether other minds exist at all.  Kant denies that knowledge relating directly to external objects or the mind is available to the knowing subject.  But on the other hand, Kant is not an empiricist in the Humean mold.  He is, rather a rationalist in the Cartesian tradition.  He resorts to non-empirical innate sources of non-sensory conceptual knowledge.

"All thought must, directly or indirectly, by way of certain characters, relate ultimately to intuitions, and therefore, with us, to sensibility, because in no other way can an object be given to us."  (Immanuel Kant.  Critique of Pure Reason (9) )

"Intuition and concepts constitute . . . the elements of all our knowledge, so that neither concepts without an intuition in some way corresponding to them, nor intuition without concepts, can yield knowledge."  (Immanuel Kant.  Critique of Pure Reason (10) )

Kant's "escape clause" was that he was still committed to an a priori presumption that there is an external reality.  But drawing upon the empirical scepticism of Descartes and Hume, Kant demonstrates that the objects of this external reality (in his words, the "nuominal world" ) are fundamentally unknowable.  In his thesis, elements of the "nuominal world" are spaceless and timeless and not directly perceptible, serving merely as the raw material from which sensations are formed.  Objects "of themselves" have no existence since space and time exist only as part of the mind, as "intuitions" by which perceptions are measured and judged.  Although he demonstrates that we can have no knowledge of such a "nuominal" world, he refuses to follow the logical consequence that Hume identified, and merely assumes that there is one anyway.  He moves away from the pure empiricism of Hume and posits that in addition to the knowledge we can gain from our sensory experiences, we have some innate sources of knowledge that guide our understanding of our perceptions. 

"I am conscious of my own existence as determined in time. All determination of time presupposes something permanent in perception. But this permanent cannot be an intuition in me. For all grounds of determination of my existence which are to be met with in me are representations; and as representations themselves require a permanent distinct from them, in relation to which their change, and so my existence in the time wherein they change, may be determined. Thus perception of this permanent is possible only through a thing outside me and not through the mere representation of a thing outside me; and consequently the determination of my existence in time is possible only through the existence of actual things which I perceive outside me."  (Immanuel Kant.  Critique of Pure Reason (11)  )

Kant is here arguing that
                    (a) My memories contain patterns of experiences;
                    (b) I cannot create those patterns myself;
                    (c) Therefore, those patterns must be generated by something outside myself.

The key step is his claim that "representations themselves require a permanent distinct from them, in relation to which their change, and so my existence in the time wherein they change, may be determined."  Kant does not see the posibility that the "permanent" he requires might just as easily be something internal.  It would be fully consistent with the rest of his analysis if this "permanent" is a sequence of subjective objects in subject time i.e. nothing more than patterns of memories.  It is a violation of Ockham's Razor to posit the existence of some sort of "actual things which I perceive outside of me".  There does not appear to be any necessity for this addition to the ontology.  All that Kant admis that he can know about such external things are the patterns of memory.  So why not just maintain that all they are is just self-generating patterns of memory.

For an Idealist to talk about finding his way around a world of "objects" that are conceived as spatially located things outside of "I", is not necessarily to concede that these objects have actual independent objective existence, external to him.  The Idealist can maintain that these "objects" are simply remembered patterns of experience, and that they are "external" to himself only in the sense that their representations are "external" to the "I" to which they are being represented.  The subject matter for perceptual judgements remains current and future experiences.  The patterns apparent in memory are given.  Perceived experiences either do or do not cohere with the given patterns in memory.  False memories and mis-perceptions are conceptually possible only from a non-Idealist perspective.

To be fair to Kant, however, his ideas were a reflection of his social environment.  At the time of their gestation (1770-ish) Man was generally considered a "Special Creation" of God.  Charles Darwin's The Descent of Man was a century in the future (1871).  Kant did not therefore consider it questionable to posit innate abilities in Man.  The difficulty with assuming that God created Man with some innate sources of knowledge, however, is that there is no logical foundation for putting any limits whatever on what God could have created in Man.  So Kant is here playing his own game of "Special Creation."  He posits that God has provided Man with whatever innate capabilities are necessary for his philosophical theories to work out properly.  And he naturally does not concern himself with the logical difficulties that this creates, or with the evolutionary foundation of such abilities.

Solipsism in Greater Detail

"Once we concede...that the immediate objects of sense experience are mind-dependent (ideas, impressions, sense data, etc.), it is indeed questionable whether we can argue validly to the existence or nature of a mind-independent external world."  (Anthony Flew, A Dictionary of Philosophy(12)  )

The Cartesian thesis that we have a more direct access to our own minds and the ideas they contain, than we do to the things "presented" by our senses, leads directly to the conclusion that what we have direct access to in sense-perception is at best the mental representation of things.  Consider the "Brain in a Vat" thought experiment.  Or, if you prefer a more science fiction example, consider a slight variation on the movie "The Matrix".  Consider the possibility that you are actually a body in a pod in "The Matrix".  In such a scenario, all of your sensory experiences are being created for you by a computer, and piped into your brain through an implant in the base of your skull.  Everything that you think you perceive in what you take to be "The world" is generated by that computer.  The world that the computer is creating you, is generated for you alone.  There is no one else in your world but you.  (The computer doesn't count.)

We can even simplify the experimental conditions.  You don't actually need a body.  All you need is a mind that can be appropriately fed with computer generated perceptions.  And the computer does not need to keep track of a long history of memories.  In addition to creating for you whatever sensory impressions are required, the computer can provide you with whatever memories are appropriate.  In that event, the "reality" that you are aware of consists of your sensory impressions of the world around you, and your memories of past sensory impressions of that world.  Perhaps, like a strange combination of the movies "The Matrix" and "Groundhog Day", you are a "Soul Pearl" imbedded in a protective pod, and every "morning" when you wake up it is the "same" day.  Your memories of "yesterday" have been wiped clean.  And if you attempt to "do" anything that the computer is unprepared to deal with, the computer puts you to sleep and resets your memory.  That way, the computer can control the "combinatorial explosion" that some people have argued would make the scenario computationally impossible.

The challenge raised by the Solipsist is that you have no means of determining whether or not you are actually in such a weird situation.  There is nothing in your experiences, and nothing in your memory, that you can use to distinguish between what you consider the "real world" (which is actually a "virtual reality" generated for you by that computer) and the "Real" world that contains both you and that computer.  If this scenario is in fact the way that things are, then as far as you can tell, there is only you and your experiences.  There is no one else.  And since you have no means of discerning the difference between the "virtual reality" in which you seem to reside, and the "Reality" that contains the computer, there is no basis from which to support the notion that the world of "Reality" actually exists.  The computer is not necessary.  The only "reality" that you have, is the discernable reality of your sensory experiences.  The rest is as fanciful as Never-Never Land, Barsoom, or Oz.

Thinking implies believing or judging things to be thus-and-so.  Such is its aim.  Thinking can either succeed or fail in achieving this aim, depending upon whether or not things are in fact thus-and-so.  One starts down the path to Solipsism when one notices that "I always have to judge things for myself."  No one else can decide for me how to interpret what I perceive, and how to respond to what I perceive.  If I take advice or information from outside sources, it is only because I have already judged those sources to be trustworthy.  Yet, if I must judge everything for myself, then there are no facts about my experiences that other people are in a better position to judge that I. 

The coherence of Solipsism is disputed on the basis that if "reality" is my experiences, then there is no possibility of an erroneous judgement about my experiences.  And hence, if there is no possibility of believing or judging in error, there is no concept of a "reality".  But this objection overlooks a number of aspects of perceptual judgement.  When I perceive something, it is automatic that I label what I perceive even if only roughly.  That labelling is a judgement that categorizes what I am perceiving into my memory of past perceptions.  If what my mind "sees" is my reality, then in that sense, I cannot perceive erroneously.  However, how I categorize that perception can easily be inconsistent with other perceptions (past, present, or future), and inconsistent with my memories of past categories of experience.  Of course, the Solipsist must assume that the soundness of her judgement is given.  Almost by definition, a Solipsist's judgement must be assumed to be rational rather than irrational, reliable rather than unreliable.  Other than the criteria of internal consistency, there is no means of discerning a systematic bias or error in the Solipsist's judgements.  In fact, other than by the criteria of self-consistency, there is no meaning to the notion of a systematic bias or error in judgement.

Because there is nothing "external", the concept of "Truth" for the Solipsist must necessarily be a "Coherence" concept.  A belief, judgement, statement or proposition is true if and only if it coheres (is logically consistent with) the rest of what I believe.  And therein lies the secret of the Solipsist's concept of "reality".  What is "real" is what is coherent with my beliefs.  A particular belief (or sub-set of beliefs) can be "false" if they do not cohere with the rest of my beliefs.  And a particular belief is corrigible to the extent that it does not cohere with the rest of my beliefs.  Moreover, because my beliefs can change as a consequence of new experiences, any particular belief (or sub-set of beliefs) is always corrigible, and can change in status from true to false (or vice versa).  Note that this is an Anti-Realist notion of "Truth".  False beliefs or judgements are false if and only if they are incoherent with the rest of my beliefs, memories, and experiences.  I can have a false belief only if there are possible experiences that could lead me to realize that such a belief does not cohere with the rest of my beliefs.  The Solipsist's acts of judgement, therefore, can be thought of  as "aiming at truth" only in the sense of a Coherence theory of truth - truth as internal consistency.

When challenged that there is no way to determine the validity of one's memories of past patterns of sensory experience, the Solipsist can respond that what matters is what I remember here-now and that these here-now memories are mutually consistent.  It is illegitimate to inquire whether my memory is in any objective sense "True" or valid.  My memory is my memory, and there is no sense in which it could be false beyond the constraints of a Coherence notion of "Truth".  However, there is every sense in which my expectations derived from those memories could be inconsistent with my actual experiences.  The Solipsist can argue that what renders such an account of memory non-vacuous is the difference between the running expectation of what we are about to experience and the actual experience, and the difference between memories that are mutually coherent, and memories that in some respect do not cohere with the rest.

So, does the Solipsist's "reality" have any more substance than a dream or an halucination, a story one makes up as one goes along?  Yes, of course it does.  Solipsist or not, the concepts of "reality" and "dream [world]" refer to two distinctly different modes of experiencing "The slings and arrows of outrageous fortune".  When experiencing life in one mode, we notice that our experiences are constant, persistent, consistent, and coherent.  When experiencing life in the other mode, we notice that our experiences are dramatically less constant in form and character, often transient in existence, frequently mutually inconsistent both from thing to thing and across time, and far more frequently quite incoherent.  One mode of experience draws the focus of our attention, is amenable to inquiry, and responsive to our reactions.  The other mode of experience often drifts uncontrollably past our attention, is rarely subject to inquiry, and is often unresponsive to our reactions.  On any scale of measure, the difference between the two modes of experience is dramatic and unmistakable whenever noticed.  One of these modes of experience we call the "real word", the other we call the "dream world" (or hallucinations, or illusions).

By definition, most of us spend most of our time experiencing life in the "real world" mode.  Episodes spent in the "dream world", while they may seem quite real at the time, always end with a transition back to the "real world" mode.  There are some unfortunate people who, for reasons as diverse as drugs to organic brain damage, spend more of their time in the "dream world".  Some people lose the ability to notice the distinctly different character of the two modes of experience, and are unable to distinguish their "real" experiences from their "dream" experiences.  But these sorts of people are classed as "not normal" or "insane".  The bottom line is that life is not a dream even for a Solipsist.  The "real world", unlike the "dream world", possesses an unmistakably greater degree of constancy, consistency, and coherence.  In the real world, elephants are huge, grey and don't fly.  In the dream world, pink elephants can buzz around your head, and turn into green mice stomping on the roof of your house.  The fact that sometimes a dream appears so real you can't tell at the time, does not alter the fact that you always wake up. 

This brings us to an approach that allows the Solipsist to identify an "objective reality".  As we have noted above, in the Solipsist's world, where reality is defined by a particularly distinct mode of experience, there are certain relatively constant, consistent, coherent patterns to those experiences that draw the focus of our attention, are amenable to inquiry, and are responsive to our reactions.  So, as a Solipsist, I can form the conceptual notions of "space" and "time" and "objects in space and time".  These sorts of concepts are convenient mental representations of particular patterns within my experiences.  I can treat these repeating patterns of experience as "Things" in my "space-time continuum".  And I can observe how they change over time, and occasionally responsd to my will.  I can observe how those "Things" interact, I can form the observed patterns of interactions the conceptual notions of "cause" and "effect".  I can even contemplate the notion of "Scientific Laws" as generalized descriptions of those interactions.  All of this, of course, is mental short-hand for observations of patterns within my experiences.  I am the only "real" existent.  The "objects" in the "world" are nothing more than conceptually grouped patterns of sensory experiences, grouped together for my own personal convenience of contemplation.  But as a Solipsist, I can none-the-less form and treat complex theories of how "Things" behave over time.  Consequently, all of science can become a part of my Solipsist reality.

Solipsist "As If" Realism

Within the on-going stream of my experiences, there are those that I find pleasurable (in various ways), and those that I find painful (in various ways).  There are obviously elements of my unfolding experiences that are not under my direct control.  In fact, I seem to have little wilful control over most of my experiences.  There are certainly elements that I do seem to be able to influence to some degree.  But most of my experiences unfold as they do regardless of any action or intention on my part.   But those experiences that occur independent of my will, stand out in absolute contrast to my freedom to act in the light of what I recognize to be the case.  Therefore, in order to maximize the pleasurable experiences and minimize the painful ones, it is obviously to my benefit to influence the unfolding of my experiences the best I can in the limited ways that I can.  However one wishes to understand the relationship, there are things I can do to avoid some painful experiences, and maximize some pleasurable experiences.

It turns out, as any moderately intelligent person (Solipsist or not) will learn after a very little bit of experience, it is very economically pragmatic (in terms of mental effort expended) to treat the unfolding of my experiences as if I were just one more object in a world of objective objects.  It turns out to be economically pragmatic to treat my experiences as if those "Things" (those convenient mental representations of particular patterns within my experiences) really did exist in "space" and "time" and behave according to those theoretical "Scientific Laws".  Amongst those convenient mental representations of particular patterns in my experiences  -  those "Things"  -  there are some that I label "people".  It turns out that influencing their behaviours in ways that will maximize my pleasurable experiences and minimize my painful ones (when considered over the long run) is easier (more probably successful, and involving less mental effort on my part) if I treat these "Things" I have labelled "people" as if they were intentional agents, with feelings and desires, very similar to my own.  Note that this is not to suppose that these "others" have the same experience of pleasure and pain as I do.  Nor is it to suppose that these "others" experience things which are "real" pleasures and pains.  As a Solipsist, I must maintain that these "others" are not things that can have experiences or psychological states  -  they are merely patterns I have identified within my experiences.  Yet, like any moderately intelligent person, I quickly discover that it is in my own interest (in terms of minimizing effort and maximizing return on investment) to treat these particular patterns within experience as if they do in fact experience the same pleasures and pains as I do, as if they do in fact have psychological states which are just as "real" as my own.  A psychopath is someone (Solipsist or not) who has not learned, or has forgotten, this lesson in pragmatic personal economics.

This is a rather strange outcome for a Solipsist.  Starting from the premise that "my consciousness is primary" we have moved through the Solipsist deduction that "I am the only existent that exists", to the pseudo-objectivist conclusion that "it will most probably pay me (in terms of maximized pleasure and minimized pain) to treat my experiences as if they were experiences of objects and people in an objective reality".

This "theoretical" identification of a "quasi-objective" reality of things and scientific laws neatly voids the Wittgensteinian argument that the existence of a public frame of reference is presupposed in the existence of the language in which Idealism and Solipsism is contemplated.  If Wittgenstein's "private language" argument is actually correct (and there is some dispute about it), the Solipsist's identification of a theoretical quasi-objective reality provides the necessary "public" forum in which a suitably public language can be acquired.

And now there is one further step.  It is readily demonstrable (according to the Solipsist's theoretical "Scientific laws" ) that it is easier to influence the behaviours of others in the ways that you want if you actually believe that they are people just like you, with wishes and wants, pleasures and pains, just like you.  Any salesman (even one who is only a convenient mental representation of a particular pattern in the Solipsist's stream of experiences) will tell you that it is an awful lot harder to sell a tale if you do not believe the tale.  So it turns out that even for a Solipsist who thinks she should believe that she is the only existent, that reality is defined by her experiences, and that what appear to be "people" are nothing more than persistent patterns in her experiences, it is economically pragmatic (in terms of maximized pleasure and minimized pain, over the long term) to actually believe like an Objectivist  -  to treat "the world" as if it was an external objective existent, independent of the mind of the Solipsist.

It is hard to deny the persuasiveness of the logical arguments following from the premises of the Inside-Out Tradition.  So even if you think the logic dictates that you should believe in Solipsism, you will never find any like minds who will agree with you.  And you will find it ultimately to your advantage (in terms of pleasure and pain) to actually believe that Solipsism is false.  Which sort of sounds contradictory, even if logically it is not.

Final Problems

It appears to be impossible to declare that you yourself are the only valid consciousness in a meaningful way, because anyone who you tell it to will automatically disbelieve you. That is a major problem for a philosopher.  It makes Solipsism workable only as a completely private belief.  It doesn't necessarily mean it isn't true.  It just means that if it is true, then none of the "people" that you identify in your experiences will agree that it is true.  If two Solipsists happen to meet, neither will accept the possibility that the other is right or even "real" (in the non-Solipsist sense).  Each will insist that "I am the only existent", and the other is therefore necessarily wrong.  After all, the other person  -  even if also an avowed Solipsist  -  is nothing more than a particularly interesting pattern in my experiences.

There is also a less immediate difficulty faced by the Solipsist.  The Solipsist concept of "the world" is based on the observation that there are quite obviously patterns in my experiences that are more or less constant, persistent, consistent, coherent, drawing the focus of my attention, amenable to inquiry, and responsive to my reactions.  But the unaddressed question is why are there patterns rather than random noise?  Why these patterns rather than some other patterns?  What, if anything, causes the patterns?  What, if anything, causes the patterns to be constant, consistent, etc.?  To these sorts of questions the Solipsist has no answer.  The patterns simply are.  And to the extent that they are constant, consistent, etc. they are self-sustaining.  Further inquiry is illegitimate.  And that sort of answer is simply unacceptable to a lot of philosophers.  Metaphysics, after all, is supposed to question everything.  And science is supposed to discover the reasons why.

Finally there is the Solipsist's concept of "Morality."  Since the Solipsist is, by definition, the only conscious entity in the world, and the other "people" with whom the Solipsist must necessarily deal are merely patterns of experiences, a Solipsist's fundamental concept of morality must necessarily be ego-centric.  This is not to suggest that the Solipsist is necessarily "Selfish to a fault", or even "Selfish first".  But it is to suggest that the Solipsist cannot properly entertain the notion that other people really do have needs, desires, and (more importantly) rights and ethical standing that are in any way similar to that of the Solipsist.  Morality, for the Solipsist, must necessarily revolve around the maximization the pleasurable experiences and the minimization of the painful ones, all with due consideration to the impact of one's behaviour on the reactions of "others" (patterns of experience tho they be), and with due consideration for the unfolding of experiences over the long term.  It is this latter caveat that opens the door to non-egocentric theories of morals.  Because the Solipsism does not control at will the experiences he has of interactions with other people, the Solipsist will quickly discover that it pays (in his own ego-centric currency) to behave (and even believe) as if those patterns in his experiences that he calls "people" actually do have ethical status equivalent to his own.  In this way, the Solipsist can "back into" a disinterested stance as a foundation for moral theory.  But this is an available option, not a necessary step.  (Unless, of course, one defines morality as granting other people equivalent ethical status as one's self.)

The Solution

So far as I can determine, neither Idealism nor Solipsism has been unquestionably refuted.  No professional philosopher likes the Solipsist conclusion to the premises of the Inside-Out Tradition.  But there are plenty of philosophers who would be ranked along with Descartes and Kant as members of the Idealist Inside-Out Tradition even if they themselves would dispute that disposition. 

If you don't like the consequences of a logically valid argument, you have only one real choice.  (I mean a logical one, rather than Hume's tongue-in-cheek pragmatic option of going off to play backgammon.)  And that is to adopt different premises.

Remember, all this started with the fundamental premise of the Inside-Out Tradition that consciousness is primary, that the mind is something separate from an objective reality, that we have a direct knowledge only of our minds and its contents and not of the source of our sensory perceptions, that there is a dichotomy between "reality" and "appearance".  This was combined with the Empiricist premise that all human knowledge derives from our sensory experiences.  So, if you don't like Solipsism as a metaphysical theory of what actually exists, adopt alternative premises.  Either, like Aristotle and other "realists", the premise of the Outside-In Tradition that existence is primary, that the mind is a product of the prior existence of reality, that we have as direct an access to the source of our sensory perceptions as we do to the contents of our mind, that there is no dichotomy between "reality" and "appearance".  Or, like Descartes and Kant, the Intuitionist premise that the mind has access to sources of knowledge other than our sensory experiences  -  innate pre-programmed ideas and concepts, or an ability to "intuit" a priori knowledge without the contribution of the senses .  Or, like Descartes and Berkeley, the Theistic premise that there is a benevolent God to bridge the gap between my mind and the "other", that we can gain from "divine revelation" knowledge not available to our senses.

In other words, if you don't want to be a Solipsist (the logical consequence of Empirical Idealism), you have to be either a Realist (of the Outside-In Tradition), or a Rationalist (Intuitional Idealism).  No professional philosopher will admit to being a Solipsist.  They have all sorted themselves into one of these two alternative groups.  So no matter which alternative you choose, you will have the company of lots of professional philosophers.  Solipsism is logically coherent in itself, but we are incapable of believing it, once the consequences of the theory are made plain.  And "believability" is the ultimate criterion of the truth of metaphysical theories. 

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Footnotes

(1)  Flew, Anthony. A Dictionary of Philosophy, New York: St. Martin's Press, 1979; pg 330

(2) Mautner, Thomas ed. The Penguin Dictionary of Philosophy, London England; Penguin Books, 2000; Pg 529

(3) Descartes, Rene, Discourse on Method, in Philosophical Writings; ed. and trans. by Norman Kemp Smith; New York: Random House, 1958, p.118]

(4) Descartes, Rene. Meditations on the First Philosophy. in The Rationalists. New York:Doubleday, 1960. pgs 121-127

(5) Berkeley, Bishop George. A Treatise Concerning The Principles of Human Knowledge, Ed. by Roger Woolhouse; New York, Penguin Books, 1988, para 1]

(6) Hume, David. A Treatise of Human Nature, http://etext.library.adelaide.edu.au/h/hume/david/h92t, Section VII, Conclusion.

(7) Kant, Immanuel. Critique of Pure Reason. Trans. Norman Kemp Smith. New York: St. Martin's Press, 1929. pg 87, B67

(8) Kant, Immanuel. Critique of Pure Reason. Trans. Norman Kemp Smith. New York: St. Martin's Press, 1929. pg 88, B68-B69

(9) Kant, Immanuel. Critique of Pure Reason, Trans. Norman Kemp Smith. New York: St. Martin's Press, 1929. Transcendental Doctrine of Elements: Introduction to Transcendental Aesthetics, A20/B34

(10) Kant, Immanuel. Critique of Pure Reason, Trans. Norman Kemp Smith. New York: St. Martin's Press, 1929. Transcendental Doctrine of Elements: Transcendental Logic, section 1.

(11) Kant, Immanuel. Critique of Pure Reason,Trans. Norman Kemp Smith. New York: St. Martin's Press, 1929. p.245, B275

(12) Flew, Anthony. A Dictionary of Philosophy, New York: St. Martin's Press, 1979; Pg 330