"As Old as Heraclitus"--Mystery Passage no. 2

The first Mystery Passage was perhaps a bit difficult. This, I fear, is too easy. But I have independent reasons for posting it. It comes from an author who declares that:

I shall take as chief stalking-horse in the discussion Professor A. J. Ayer's The Foundations of Empirical Knowledge; but I shall mention also Professor H. H. Price's Perception, and, later on, G. J. Warnock's book on Berkeley. I find in these texts a good deal to criticize, but I choose them for their merits and not for their deficiencies; they seem to me to provide the best available expositions of the approved reasons for holding theories which are at least as old as Heraclitus--more full, coherent, and terminologically exact than you find, for example, in Descartes or Berkeley.