In his text Realism and Truth(1), Michael Devitt argues that metaphysical realism is the only rationally justifiable metaphysical attitude. Devitt employs the method of abduction(2) (the process of reasoning to the best explanation).
Drawing upon his arguments, and adding my own twist, I would argue that Metaphysical Realism is the best available metaphysical explanation for our perceptual experiences because:
1. Metaphysical Realism is the simplest and best confirmed hypothesis that accounts for the patterns we appear to experience in our experiences. Admittedly, all the information we can gain about the external world is gained through our perceptions, our experiences. So it is logically acceptable to posit that all that exists is our experiences -- the Solipsist posit. But even the Solipsist, and the Kantian, and Berkeleian Idealists, must admit that there are patterns to our experiences that are mysteriously inexplicable without the posit of some form of mind-independent reality (even BErkeley assumes a God independent of our mind). If all alternative metaphysical attitudes must eventually end up behaving towards reality as if it were an objectively existing and mind independent reality, then in the absence of any evidence to the contrary, the simplest explanation is that reality is in fact objectively existing and mind independent as metaphysical realism maintains.
2. There is a monstrous emotional and psychological difference between thinking that the other person is but a useful construct consisting merely of patterns in ones experiences, and thinking that the other person has independent objective ontological existence. Ultimately, all forms of subjectivism are either forced into the former position, or forced to adopt a "free-floating" premise that is logically inconsistent with the initial subjectivist premise. Metaphysical Realism is the only metaphysical attitude that is both logically consistent and acknowledges the independent objective metaphysical existence of "The Other".
3. The language of realism is necessary to permit communications even for philosophers. The common language (English for us) is configured for realism. To talk about any alternative metaphysical position, the initiator must start by employing the common language of realism. An argument for any alternative metaphysical attitude will almost inevitably involve the idiosyncratic redefinition of common English words to mean something quite different and almost always confusing.
In summary, then, we have the First Axiom of Evolutionary Pragmatism that there is a Reality that is objective (independent of any observer or observation), constant (permits repeatable observations) and self-consistent (does not exhibit mutually contradictory cause-effect relationships). As a consequence of this axiom, Evolutionary Pragmatism regards Reality as deterministic (non-random) and subject to comprehensible cause-effect relationships that may be studied, understood, and used to predict the future behaviour of Reality to a useful degree. Of course, this does not mean that Evolutionary Pragmatism considers Reality to be, at this time, perfectly understandable or totally predictable. Evolutionary Pragmatism accepts both the Heisenberg Uncertainty Principle (that we cannot know, even in principle, the "position course and speed" of all particles), and the principles of Chaos Theory that result from the operation of non-linear dynamic systems.
Drawing upon the best understanding available of human behaviour, we can see that the Mind initiates action from three different levels: instinct, habit, and reasoned choice. Observing the extent to which modern Man is governed by human cultural patterns, life-styles, philosophies, and pure mental laziness, it would appear that the habitual behaviour patterns are the more prevalent of the three. But when it does come to the Reasoned Choice decision, we have seen that a "Successful" decision depends directly on the amount of knowledge that the individual has gained about the nature of Reality, and the degree to which the individual can predict the consequences of his/her actions. Although a Reasoned Choice behaviour is one that is selected and initiated through conscious decision processes, it is also heavily influenced by the output from the instinctive Emotional processors that generate the individual's emotional needs.
Reasoned Choice behaviour also, of course, depends on the nature of the individual's Value Patterns, and I will talk more about what these are, and how they impact the definition of "Successful" decision making when I talk about Ethics. But key to both the creation of Value Patterns, and a useful understanding of the behaviour of Reality, is the processes of Learning and the acquisition of knowledge. So I will turn my attention now to the definition of Truth that distinguishes fact from fiction, and the definition that distinguishes opinion from knowledge.
(1) Devitt, Michael. Realism and Truth, 2nd Edition. Princeton University Press, Princeton, New Jersey. 1997. ISBN 0-691-01187-7.
(2) Wikipedia contributors, 'Abductive reasoning',
Wikipedia, The Free Encyclopedia,