One of the earliest theories of epistemology is attributed to Heraclitus. His theory can be summarised in the phrase “everything is in motion.” Because we lack a complete text attribute to Heraclitus, much of our information is based on fragments and secondhand sources. One of our best sources comes from some of Plato’s writings, particularly his Theaetetus. As such, we’ll be working from the assumption that Plato was accurate in his understanding of Heraclitus’s theory.
Plato‘s Theaetetus will be a focus in many of the discussions on epistemology because (1) it is Plato’s clearest work on the matter and(2) Plato covers many different views that eventually become their own theories. If you don’t have a copy available, there is a good summary at the Stanford Encyclopedia of Philosophy [link] and a copy at Tuft’s Perseus Library [link]. i’ll follow the standard pagination. This one dialog is quite possibly Plato’s clearest discussion on the matter as it revolves around the question, “What is knowledge?” The first third or so of the dialog, Theaetetus suggests that knowledge is perception. As such, Socrates takes this definition and compares it to Protagoras‘s notion that “Man is the measure of all things: of the things which are, that they are, and of the things which are not, that they are not” (this will abbreviated as “Man is the measure” or MM). In combining these two notions, we are left with a more defined (and arguably stronger) position. There are some problems with this, though. Socrates quickly discovers that if man is the measure, then something “heavy” could appear “light” to someone. Therefore, it seems that this view, when considering some form of “objectivity,” requires more. As such, Socrates suggests that things are not, but rather are becoming. That is, things that are objects of perception are relative to each other. Six dice, when placed besire four, is “more,” but when placed beside twelve, is “less.”
Yet, Plato does not end there. He comes to Protagoras’s defense and remakes Protagoras’s argument, adding the requirement of compentcy. That is, a person can “judge rightly” with MM relative to his competency on the matter. Therefore, someone who is a medical doctor would generally have a more correct opinion on matters of medicine than a baker. So, Socrates introduces another problem: the future. In one example, he has a person come to a doctor and claim that he will have a fever in the near future and the doctor disagrees. If “man is the measure,” then we have a problem: the future cannot hold both claims to be true. We cannot accept the possibility that the man will have a fever by his measure, while not by the doctor’s measure. There is no amount of competency that would allow a doctor to accurately determine whether a healthy person will have a fever in the near future. This problem is reflected in Hume’s argument in An Enquiry Concerning Human Understanding. There is no guarantee that two events occuring immediately after one another (say lightning and thunder) must occur that way in the future. This has become an accepted view in science, even though it is impractical. As such, Plato rejects MM in its current state.
Socrates tries then to look at the problem through Heraclitean flux: that everything is in motion. This view argues that a given object (say this word) is in constant motion such that at any given moment, it can be any color. If i were to call it “green” while another calls it “red,” we would both be correct because the object had to be that color in the moment of perception. This is based on the argument that flux must be seen in two ways: (1) change in position (i.e. physical motion) and (2) change in appearance. For flux to work, everything must be in both forms of motion, else it would be in motion while standing still. Physical motion can be seen in recent physics through Heisenberg Uncertainty Principle which does suggest that everything is in constant physical motion (even stationary objects have a very minute level of motion). In fact, if something had no physical motion, it would have no temperature (i.e. it would be at absolute zero) because temperature requires motion. Thus, if we are to speak of things that are in constant motion, we are unable to speak thusly about them. This would then make the kind of language necessary to be correct about a particular perception unitelligible. Socrates then argues that we are completely free from the notion that “knowledge is perception.” Yet, we still have one problem: Parmenides. The Parmenidean theory suggest that everything is one and totally unmoved. In other words, reality is not in motion at all and any perceived motion is imaginary. Zeno agrees with his mentor here (cf. Zeno’s Paradoxes). Yet, it should be self-evident from above that this position is also untenable, particularly in contemporary thought. Is there some middle ground in which we can find an answer? Can we navigate between Scylla and Charybdis? We’ll have to look somewhere besides “knowledge is perception.”