Skepticism is an important component of Socratic/Platonic reasoning, perhaps even its distinguishing part. (A later iteration of the Academy founded by Plato, an iteration which began with a shift of emphasis by its then director Arcesilaus around the middle of the 3rd Century BCE, was called in fact “The Skeptical Academy”.) It must be noted however that the root verb skeptsesthai means something more like “to conduct an investigation” than “to deny all positive assertions.” To be skeptical in the Platonic sense does mean to tease out the negative features, the defects, that haunt all honest attempts to assert what is true. But such skepticism, on discovering the dubious and defective, does not necessitate an unqualified denial. Thinking through opinion, a mode of cognition that Plato called dianoia, requires that we continue to hold the limited positive senses of assertions while remaining open to the anterior norms that make awareness of the negation possible. Opinion is an intermediate, a metaxy, between ignorance and knowledge. Participating in both, opinion always both reveals and conceals, indicates and detracts from knowledge. From the Divided Line, it is clear that as image stands to object, so in dianoia does opinion stand to truth. Both the positive anticipation and the nagging doubts are signs that witness to the true and “we have no power of thinking without signs” (C.S. Peirce).
A failure to understand a medium as a medium, a mistaking a means for an end, does enormous epistemological mischief. This failure is particularly acute when coupled with strong enforcement of the “Law of the Excluded Middle” — the “law” that claims that a proposition is either true or false simply with no third option. Descartes’ chief error is in restricting the realm of truth to those things that could be known with certainty, rejecting as false all statements that are in any way dubious. It is an error to reject as wholly false that which is in some sense true. But the realm of the excluded middle, the realm of what could be true but may not be, is a rejection of doxa as such, a rejection of the the only medium through which knowledge of the existentially vital may be approached. Although the abstract can be known with certainty, even this certainty breaks down when we attempt to apply it to the concrete world. Dianoia is a moderate position between rival errors: to reject as wholly false what is in some sense true, and to accept as uncritically true what is still open to doubt or error. Either of these stances is arbitrary and blind.
Thinking has a from-to character of the type that Michael Polanyi describes: “The subsidiaries of from-to knowing bear on a focal target, and whatever a thing bears on may be called it’s meaning. Thus the focal target on which they bear is the meaning of the subsidiaries.” (Personal Knowledge, p. 35) To look *at* the opinion without looking *through* it (the “dia-” of dianoia) is a failure to understand what it is. (Plato’s hypothesis of the Forms is often a victim of this type of misreading.) In a Platonic examination — the skepsis of an honest opinion — the misgiving/doubt that inevitably results is not a bug but a feature.