Modern philosophers studying epistemology generally distinguish between three different kinds of "knowledge". They identify what is called "acquaintance knowledge", "ability knowledge", and "propositional knowledge". Plato's concept of knowledge would have to be classified as "acquaintance knowledge". It is also clear from his dialogues that he considers knowledge to be certainly and indubitably true. As well, Plato takes a very Heraclitean view of the sensible world, and he reserves his concept of knowledge to the unchanging world of the Forms.
Ability knowledge can be exemplified by such claims as "I know the violin". This sense of the word implies some special skill or ability. It is "knowledge how . . .". Plato does not address abilities within his concept of knowledge. In the Meno dialogue, when Socrates is discussing with Meno the difference between knowledge and true opinion, he draws a clear distinction between one who has a true opinion about the way to Larissa but has never been down that road, and one who "knows"the way to Larissa because he has been down that road and is familiar with (is acquainted with) the road. So to Plato, one who knows how, without being familiar with the ability, has true opinion rather than knowledge.
Acquaintance knowledge is the kind of knowledge we claim when we are familiar with a person, place, thing, (or road to Larissa). It is "knowledge of . . .". For example, I can claim to "know"the way to Larissa if I have been down that road, and can recall how to navigate my way from here to there without error. Acquaintance knowledge is very similar to ability knowledge in that it involves the ability to recognize what has been previously encountered. As Bertrand Russell describes knowledge by acquaintance, "we have acquaintance with anything of which we are directly aware, without the intermediary of any process of inference or any knowledge of truths."(1) As he put it, "I say that I am acquainted with an object when I have a direct cognitive relation to that object, i.e., when I am directly aware of the object itself."(2)
Propositional knowledge, by comparison, is "knowledge that . . .". Propositional knowledge is what Russell describes as "knowledge by description". Descriptive knowledge he claims is derivative -- it is based on both an acquaintance with things, and a knowledge of truths. It is these truths that distinguish propositional knowledge. Such truths appear in statements that have the general format "S knows that P", where "S"is any particular subject of interest, and "P"is some belief (usually conceived as a proposition or other truth carrier -- philosophers differ) that describes some characteristic of Reality. Traditionally, in modern epistemology, it is "knowledge that"that is the focus of theories of knowledge. Knowledge as acquaintance, "knowledge of", is not usually included within the scope of such thinking.
Plato's concept of knowledge, as we would expect, pre-dates the divisions of modern epistemologists. Although his concept evolves somewhat over the course of his dialogues, it remains clearly centered on what we would today call "knowledge as acquaintance". In the early "Socratic"dialogues, Plato relates the search by Socrates for the meaning of such concepts as "virtue", "goodness", "justice", and the like. Throughout these dialogues, Socrates repeatedly professes ignorance of the proper answer, but searches for that common element or aspect of things that renders "virtuous"those actions we call virtuous, "good"those things we call good, or "just"those things we cal just. He seeks the basic common principle of that "virtue", "goodness", or "justice"that we recognize to exist in those things we call virtuous, good, or just. In other words, Plato is here employing an acquaintance concept of knowledge. Socrates is familiar with many things that are virtuous, good, or just. He seeks to become directly aware of the common underlying factor that he will recognize because of that familiarity.
In the Meno and Phaedo dialogues, Plato presents his theory of knowledge as recollection of something with which the soul is already acquainted. In a key scene in the Meno, Socrates draws upon one of Meno's slaves in order to demonstrate his Theory of Recollection. By showing that the slave can display "knowledge"of things he could never have learned, Plato attempts to demonstrate that knowledge can be recollected. Suitably guided, he suggests, if one learns one point, it is possible to "recollect"all of the rest (Meno 81d). In the Republic (Book IV) Plato repeatedly employs the metaphor of sight or seeing to describe the kind of knowing that takes place in the realm of the Forms. In the allegory of The Cave, for example, he employs the metaphor of the Sun casting light upon things knowable. Knowing is characterized by direct presentation, or confrontation, with the objects of knowledge. And this is, of course, exactly what is meant by "knowledge of" -- knowledge as acquaintance.
Despite his metaphor of seeing in the Republic, what Plato fails to do in his arguments for the recollection theory of knowledge in the Meno nd the Phaedo, is provide any suggestion of how the soul comeds by its "direct cognitive relation"with what it supposedly later "recollects"(the Forms), even granting the hypothesis that it gains its acquaintance with the Forms in the "other world". One has to provide the missing reasoning and interpolate that the soul, before birth, must somehow "encounter"the Form that is to be later recalled to mind. It requires the assumption of the notion of "knowledge as acquaintance"to make the recollection theory comprehensible. The modern context of "knowledge that"renders the recollection theory of knowledge superfluous.
In the Timeaus, Plato claims that knowledge is of what is exempt from becoming (Timeaus 27d-28a). Since sensibles are not exempt from becoming: there can be no knowledge of them (Timeaus 52a). Knowledge, therefore, must be of something unchanging -- the Forms (Timeaus 52d). In the Phaedo, where he introduces his Theory of Forms, he maintains that they are exempt from change, while sensibles always change (Phaedo 78d). Sensibles suffer becoming and perishing (Republic. 485a, 508d, 521d, 534d, Symposium 210e, 211a). He employs similar arguments in the Republic (479a-d) to show that sensible things, because they are always changing, cannot be the primary objects of knowledge.
The most critical consequence to the concept of knowledge as recollection of things the soul has encountered in the unchanging realm of the Forms, is that "knowledge"is only possible of a priori things. To draw upon the often problematic "analytic / synthetic"dichotomy -- Plato's recollection theory is conceivable only for analytic (a priori) knowledge -- knowledge that is inherent in (logically deducible from) the data already available. That two sticks (with lengths already in hand) are equal is determined from the meaning of the word "equal". The recollection theory is totally incompatible with synthetic (a posteriori) knowledge -- knowledge that is dependent on investigation of the world around us. In numerous places throughout the dialogues, Plato reinforces this reservation of the concept of knowledge to the a priori by emphasizing the changeability, and hence unknowability, of common sensibles.
The other key consequence of a concept of knowledge as restricted to the unchanging realm of Forms is that knowledge is necessarily both eternal and certain. Knowledge is eternal, because all things with which one can be come acquainted in the Realm of Forms are by stipulation eternally unchanging. Nor is there any opening for error in Plato's concept of knowledge, because the direct cognitive awareness involved is unmediated by any judgements that might be erroneous.
By the Theaetetus dialogue Plato's concept of knowledge has evolved more towards what we would now call propositional knowledge. And it is Plato's third analysis in the Theaetetus that is generally recognized as being "Plato's definition of knowledge."By comparison to the passing treatments of knowledge in the earlier dialogues (particularly the Meno and Phaedo), in the Theaetetus it is Plato's entire purpose to examine some competing ideas about knowledge. Oddly enough, however, nowhere in the Theaetetus does he examine his own earlier supposition that knowledge is recollection. The closest he comes is in his rejection of the theory of knowledge as perception in the first analysis of the Theaetetus. While this reinforces the restriction that Plato imposes by reserving knowledge to the realm of Forms, it does leave problematic the means by which the soul gains its acquaintance with the Forms (if not be perceiving the Forms, then how?). To properly understand the theory of knowledge that he introduces in the Theaetetus, it remains always necessary to keep firmly in mind the framework he has established of knowledge as acquaintance, and knowledge as limited to the Forms.
Plato is nevertheless credited with the earliest documentation of the now
generally accepted standard "Tripartite"definition of "knowledge": -
S knows that P if and only if
(i) P is true; and
(ii) S believes that P; and
(iii) S is justified in believing that P.
Knowledge is therefore a special kind of belief, a belief that satisfies some additional conditions. In order to be knowledge, a belief must not only be true, it must be accompanied by some form of "account" ("logos"). The key difficulty that Plato identifies with this definition is the proper understanding of "account" (or "logos"). Or in modern parlance, the proper understanding of just what constitutes the necessary "justification"that qualifies a true belief for the honorific of "knowledge".
In the Theaetetus (206c-210d) Plato goes through three suggested explanations of how to understand this "account"(or "logos"). He is satisfied with none of them, criticizing each in turn, and leaving the issue unresolved at the close of the dialogue. The most complete of the three is the third - he proposes that to give the "logos"of one's belief that P is to cite the manner in which P differs from everything else, or everything else of P's kind. So knowledge of (say) Theaetetus consists in true belief about Theaetetus plus an account of what differentiates Theaetetus from every other human.
Keeping in mind that Plato views knowledge as an acquaintance of Forms, it is problematic just how to understand his suggestion. Interestingly, although he uses Theaetetus (clearly a sensible, in this world at least) in the example he cites, the true beliefs about Theaetetus that would qualify for knowledge by Plato's concept would all have to be about the Form of Theaetetus (presuming there is one -- not a foregone conclusion) rather than any sensible properties of the sensible Theaetetus. Just what might be a manner in which the Form of Theaetetus differs from the Forms of other humans, or the Form of Man, is therefore an interesting problem. One that Plato unfortunately provides no guidance for.
Combined as it obviously must be, with Plato's Theory of Forms, his concept of knowledge leaves it highly problematic just how we are to have knowledge of anything. And it particularly disavows most of what we commonly call knowledge -- empirical "knowledge"like that I have two hands. Plato's concept of knowledge is thus rendered less than useful for common discourse, and restricts his concept of knowledge to the specialized field of Platonic philosophy. But within that limited field it does, for example, make quite comprehensible Socrates'repeated claims to know nothing -- by Plato's concept of knowledge it would be difficult to understand how Socrates could actually "know"anything at all. And it similarly renders comprehensible Socrates'search for the definitions of virtue, goodness, justice, etc. What he is seeking is the "logos" -- the factor that distinguishes the Forms of Virtue, Goodness, Justice, etc. from all the other Forms. On the other hand, it renders problematic the use Socrates makes in the Cratylus of his "knowledge"(or perhaps it should be "opinions"?) of the etymological derivations of so many Greek words -- clearly empirical knowledge if anything is.
(1) Russell, Bertrand. The Problems of Philosophy. Oxford University Press. Oxford, England. 1912. Pg 46
(2) Russell, Bertrand. "Knowledge by Acquaintance and Knowledge by Description"in Mysticism and Logic, Doubleday Anchor Books, New York, New York. 1957. Pg202.
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