We cannot assert the existence of “what is not” without contradicting ourselves. Parmenides of Elea came up with this conversation‐stopping argument about two‐and‐a‐half millenia ago, and used it in showing that, contrary to how we “erring mortals” tend to interpret the evidence of our senses, reality is necessarily single, unchanging, and indivisible (On Nature). Protagoras of Abdera (c. 490‐420) seems to have thought that the world is just as it appears to the senses of mortals; his treatise On Truth, of which only fragments survive, begins with the famous words: “Of all things man is the measure”.
These two intellectual titans are discussed here in chapters on Pythagoreans and Eleatics and The Sophists respectively. There are a dozen, broadly chronologically‐arranged chapters, each written by a different academic specialist and supported by extensive scholarly notes and bibliographies. In a chronology at the front of the book the earliest date of philosophical significance is 585 bc, when Thales is said to have accurately predicted a solar eclipse. At the back are a glossary, an index of topics, an index locorum, and an index of proper names.
The last three chapters are devoted to Plato. In the introduction C.C.W. Taylor notes that Plato accepted Parmenides’ view that “only the objects of thought, as distinct from perceptible things, are fully real”, but tried to show “how the observable world is an approximation to ... the intelligible world”. Catherine Osborne argues that the multiplicity of interpretations of the Heraclitus fragments illustrate this mysterious thinker’s fundamental insight, which is that “what counts as the same and what counts as opposed is decided by a significance acquired in a social or temporal context”. In the chapter on the sophists, G.B. Kerferd observes that Protagoras’ homo mensura doctrine has been taken to imply that “whatever seems right to any one individual is necessarily and infallibly right for that individual”, which has “clear echoes in present‐day thinking about values”.
I have now looked into the first and the last volumes of the ten‐volume Routledge History of Philosophy, and I have learned a lot from both of them. Karl Popper followed Aristotle in complaining that for all his talk about “the Good” Plato did not tell us “what we ought to do” (“Plato: ethics and politics”). A.W. Price suggests that “in a manner, the Republic deconstructs itself”; the figure who is formulating the principles of a perfectly co‐operative community ‐ Socrates ‐ compares himself to a blind man, though he believes he is on “the right road”.
