It has been alleged by many commentators that Plato never developed a precise philosophical vocabulary, and this view is strengthened when one investigates the employment of many of Plato's key terms: εἶδος, ἰδέα, αἴσθησις, δόξα, to name but a few. In the early and middle dialogues, Plato uses these terms in a variety of contexts without giving the slightest indication of which of the many possible senses is to be understood. Indeed, in the Euthydemus, Socrates is represented as ridiculing those who attempt to draw precise distinctions for they ‘… would only be able to play with men tripping them up and oversetting them with distinctions of words’ (Jowett, 278). Yet one must be cautious in simply assuming that Plato never attempted to clarify the meaning of his central philosophical terms; in particular, one must note that the Theaetetus contains several attempts to mark off various senses of λόγος, and that the entire dialogue is directed toward a precise account of what is, or ought to be meant by ‘knowledge’. Thus while it is true to say that Plato usually fails to mark off distinctions between various senses of the same term, the Theaetetus shows that this is not always the case.
In this paper, I shall argue (1) that Plato attempts to separate two distinct senses of the comprehensive Greek term for knowledge, εἰδέναι, reserving γνῶσις for what we should term ‘knowledge by acquaintance’ and employing ἐπιστήμη for ‘intellectual knowledge’ or ‘knowledge that something is the case’, and (2) that the statement and refutation of Socrates' dream theory in the Theaetetus show this.