Lecture Notes, UC Davis Philosophy 102, Theory of Knowledge

Ancient Epistemology

G. J. Mattey, Senior Lecturer

Plato Sextus Empiricus

Texts: Meno, Theateteus selections, The Republic selections, Plato. Outlines of Pyrrhonism, Sextus Empiricus

Plato, writing in the 4th century BCE, was the first western philosopher whose surviving writings deal extensively with knowledge. The main places where he discusses knowledge are in his dialogues Meno, the Republic, Phaedo and Theaetetus. We will discuss excerpts from three of these works. In the 2nd century CE there appeared a compendium of skeptical arguments by Sextus Empiricus, entitled Outlines of Pyrrhonism. We are in possession of several other skeptical books by Sextus. Here we will be concerned with the opening book of the Outlines.

What is Knowledge?

Following his teacher Socrates, Plato was concerned to discover what things are. He asked this question concerning many matters, including justice, virtue, piety and knowledge. In the Theaetetus he sets as a task to "try to find a single formula that applies to the many kinds of knowledge" (148d). There is a presumption by Plato that there is a single thing, knowledge, which should be capable of being defined. This presumption is shared by contemporary analytic philosophers who seek a single set of necessary and sufficient conditions for someone to know something.

The first attempt at finding a definition equates knowledge with perception. In our text we have an excerpt in which Socrates attempts to prove that "perception and knowledge can never be the same." After reaching this impasse, Plato discussed some further definitions: true judgment, true belief, and true belief with the addition of an account (logos). All are rejected. Contemporary analytic philosophers have spent much effort examining the analysis of knowledge as justified true belief. This bears at least a superficial similarity to the last of Plato's proposed definitions.

Knowledge as Perception

There is a strong intuitive pull to the idea that if someone perceives something, then he knows that it is the case. (The converse, that if one knows that something is the case, then one perceives it, seems too limited for serious consideration.) Suppose I see a red apple before me. That is, there is a red apple before me, it causes changes in my sense-organs and these changes are communicated to my brain, resulting in a perception of the apple. Why not say that there is knowledge through the very act of perception?

The basic answer to this question we can glean from the Theatetus is that the perceptual process lacks an intellectual dimension. If I am to know that there is a red apple before me, I must have an intellectual or conceptual grasp of what an apple is, what my body is, and what the relation of the apple to my body is. Contemporary philosophers generally say that the highest form of knowledge (certainly the kind Plato had in mind) involves propositions. In the present case it is the proposition that there is an apple before me. Propositions, in turn, are composed at least in part of general concepts such as the concepts apple and in front of. Perception concerns only what is specific, not what is general, and so it is not propositional knowledge.

Plato puts it this way. We receive information from various sense-organs, so that there needs to be some central faculty to grasp what is in common in the output of the senses. This is the soul itself, and it moreover grasps higher-level concepts such as likeness/unlikeness, identity/difference, existence/non-existence. These are all required for an understanding of truth, which requires reasoning by the soul. So since knowledge requires an understanding of truth, it requires the non-perceptual process of reasoning, whch in turn requires intellectual mastery of concepts.

Note that Plato considered knowledge to be a single thing, just as are beauty and justice. We might want to allow that there is a form of knowledge that is not conceptual, at least to the extent that it does not require an intellectual awareness of the meaning of concepts. Thus, we might want to concede that birds have instinctive knowledge of nest-building or perceptual knowledge of food.

Knowledge and True Belief

As was mentioned above, Plato rejected the equation of knowledge with true belief. His reason is that a jury which judges a case based on hearsay may have true belief but lacks knowledge because knowledge requires eye-witness testimony. "But if true belief and knowledge were the same thing, the best of jurymen could never have a correct belief without knowledge. It now appears that they must be two different things" (Theaetetus 201c). In the Meno, Plato explores further the relation between knowledge and true belief (which is here called "opinion").

We might ask ourselves what practical difference it would make if the jury convicted a person based merely on true belief rather than on knowledge. The guilty person will be punished in either case. An obvious response is that knowledge is a better standard in a jury case because admitting a lower standard will over the long run result in many convictions of innocent persons. (In fact, knowledge could just as well turn out to be too high a standard.)

Plato deals with this issue in the second selection from the Meno. Meno raises roughly the objection we have just rehearsed: that opinions that fall short of knowledge cannot be counted on to be true in the long run. "The man who has knowledge will aways succeed, whereas he who has true opinion will only succeed at times." But Socrates counters this response with a question: "Will he who has the right opinion not always succeed, as long as his opinion is right?" In the jury case, we can say that the issue is not whether hearsay evidence is strong enough to warrant conviction, but rather whether true hearsay evidence, which will always issue in a proper verdict, is strong enough to warrant conviction.

Meno then asks Socrates why knowledge is prized, given that right opinion is always successful. The reason, Socrates responds, is that right opinion itself is not stable. Take the case of hearsay evidence. Sometimes it will produce right opinion and sometimes it won't. An eye-witness report, however, establishes a more direct link between the event in question and the opinion. In the Meno, Socrates says that the missing element in mere right opinions is what "ties them down by [giving] an account of the reason why." So "knowledge differs from correct opinion in being tied down."

Note that this is not quite the same as saying that knowledge just is correct opinion that is tied down by an account, a claim that Plato rejected. All Plato claims here is that knowledge is tied down and correct opinion is not. Also note that Plato did not bring up the jury case in the Meno. He may have thought that although an eye-witness account is necessary for knowledge, it is not sufficient.

A Priori Knowledge

In fact, it seems that Plato would never have allowed that the jury has knowledge. In the Republic, he claims that sensible objects and events (like the commission of a crime) are stuck at the level of true opinion. The reason is metaphysical. For Plato, the true reality lies in the forms (most particularly in the "idea of the good"), while the sensible world is a kind of shadow-image of true reality. The relationship between the two is illustrated vividly in the analogy of the cave. (This general approach was pioneered earlier by Parmenides.)

With respect to knowledge, there are two main problems with the world of the senses. The first is its instability. Things change from one kind of thing to another. Plato seems to have thought that this kind of impermanence makes the sensible world unsuitable for knowledge. "When [the soul] inclines to that region which is mingled with darkness, the world of becoming and passing away, it opines only and its edge is blunted, and it shifts its opinions hither and theither, and again seems as if it lacked reason." How can I know that a thing is of a kind, when it might just as well become another kind at some other time? (Contemporary philosphers would answer that our knowledge need not extend over time, but instead may be restricted to the way things are at a given time.)

The fundamental problem with the world of the senses is just that it is grasped by the senses, not by reason. Now we saw before that Plato seemed to allow that true opinion could become knowledge if supplied with "an account of the reason why." But the ultimate reason why will always be lodged in the world of the intellect. There is always room for error in the application of the reason to the issue at hand. Only when the reason itself is the object do we have knowledge, that is, do we have something that is tied down.

So how is knowledge of the objects of intellect tied down? In the Meno, Plato tells us that it is by "recollection." Plato tells us that the soul was in direct contact with the forms before birth and thus knew them. (Compare the jury case, where knowledge calls for eye-witness testimony.) But when it became encumbered by a human body, it forgot this knowledge. The rediscovery of the lost knowledge is recollection.

In the Meno, Plato tries to demonstrate that it is possible to recollect the forms. He tries to show how a slave-boy who is ignorant of the Pythagorean theorem nonetheless can be led to recognize the truth of one of its instances simply through questioning without any instruction. Socrates lets the boy try to come up with the length of the diagonal of an isosoles triangle whose sides are two units long. He fails, and Socrates leads him to a construction from which the answer can be seen pretty readily.

There are problems with this argument. In the first place, the boy did not produce the construction on his own. Secondly, even if he were able to recognize the correct answer based on the construction, there is no need to attribute this to recollection. He could have come to this conclusion based on what knowledge he had gained during his life, combined with the ability to reason.

Since Plato's time, many philosophers have embraced his view that we have knowledge indpendently of experience. Such knowledge is called "a priori," following the eighteenth century philosopher Immanuel Kant. Descartes held a view of this kind, which we will examine in the next lecture. After that, we will look at an account of a priori knowledge by a contemporary philosopher, Philip Kitcher.

The Problem of the Criterion

After the time of Plato, numerous schools of philosophical thought competed for supremacy. Among the schools were those of Plato's student Aristotle, of Epicurus, and of Zeno the Stoic. The inconclusive rivalry of these schools suggested to some philosophers, skeptics, that there is no philosophical knowledge to be had. Each view had its own reasons to support it, yet each was contradicted by another view with its own supporting reasons. There was no agreement.

It appeared to some of the skeptics (we do not know exactly which ones) that there was no prospect for agreement. An argument, known as "the problem of the criterion," was offered to support this view. If agreement is to be found in a reasonable way, there must be some standard or criterion by which to settle the disputes. Otherwise, the fact of disagreement indicates that we should suspend judgment.

But it is clear that we are not yet in possession of such a standard, since the dispute remains unsettled. Each side has its own standard according to which its own view is correct. There is, then, "a dispute about standards." To settle this dispute, we are in need of a standard. Each side will pick its own standard to settle the dispute about standards. In this way their defense is circular (or "falls into the reciprocal mode"). This means that there is no settlement of the original disputes.

One might try to evade this result by introducing a new standard for judging the standard. Everything would then be pushed to a higher level. This has the danger of leading to a never-ending procession of standards of standards of standards, etc. In that case, there is no agreement. Another way approach would be just to assume a standard arbitrarily. In that case, there would be no agreement either, since that standard would no doubt be chosen to favor one's own philosophical theory. Moreover, the standard would have no rational basis.

This argument is very powerful, but few philosophers have tried to cope with it. Many debates in contemporary theory of knowledge seem to founder just because there is no agreed-upon standard for evaluating theories. The discussion of methodism and particularism in the last lecture illustrates the point. The debate between "internalism" and "externalism" to be discussed later reinforces it. It seems that theorists of knowledge are willing to "agree to disagree," while being convinced that they are right and trying to sway as may people to their side as they can.

Pyrrhonian Skepticism

The problem of the criterion was just one of a vast array of skeptical weapons described in Sextus Empiricus's writings. The skeptics who developed these arguments were known loosely as "Pyrrhonian," after Pyrrho of Ellis, who lived at the turn of the third century BCE. Attempts had been made by the Pyrrhonians to systematize these arguments. In our text, we have parts of a group of ten skeptical ways or "modes" of arguing. Generally, the modes exploit the fact that different people's situations are different. These differences, it is argued, preclude people from having knowledge.

The third mode concerns internal differences the various apparati of perception. Our different sense organs deliver different information. Which reveals the reality of things? Does the thing have a quality corresponding to each type of perception? A single quality that appears differently to all sense-organs? Or more qualities than we have sense-organs to judge? If we try to answer that question by a theory of how the sensory apparati are fitted to nature, we must face the disagreement in theories as to how this takes place.

The fourth mode is perhaps more familiar, having to do with differences in the circumstances of perception. Sextus gives us examples that pop up again and again in early modern philosophy, such as the fact that honey tastes sweet to someone in good health but bitter to someone with jaundice. If we try to apply a standard of "normalcy" such that the "normal" person correctly detects the quality, we find ourselves in disagreement and faced with the problem of the criterion. This problem arises with the other modes discussed in the text.

Faced with this array of skeptical arguments, the Pyrrhonian suspends judgment with regard to those matters on which there is disagreement. He does not go so far as to disbelieve everything, though. There is still room for judgments about the way things appear to him. What is proscribed is assent "to some unclear object of investigation in the sciences. The Pyrrhonists do not assent to anything unclear." When the skeptic professes a belief, it only a report of "their own feelings without holding opinions, affirming nothing about external objects."

A skeptic still has to live (though it has been reported that Pyrrho was indifferent about his welfare). To this end, he adopts the customs and practices of the places in which he finds himself. The end result of skepticism is tranquillity.

A final comment is that the skeptics profess not to deny dogmatically that there is knowledge, but rather to be "still investigating." Perhaps some day there will be total agreement on the qualities of objects. The skeptic does not think this will happen given the massive disagreement that exists today.

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