What now does Plato mean by idea? From what has already been said it is clear that he means something more than ideal conceptions of the beautiful and the good. An idea is found, as the name itself (εἰδος) indicates, wherever a universal conception of a species or kind is found. Hence Plato speaks of the idea of a bed, table, strength, health, voice, color, ideas of simple relations and properties, ideas of mathematical figures, and even ideas of not-being, and of that, which in its essence only contradicts the idea, baseness and vice. In a word, we may put an idea wherever many things may be characterized by a common name (_Rep._ X. 596): or as Aristotle expresses it (_Met._ XII. 3). Plato places an idea to every class of being. In this sense Plato himself speaks in the beginning of the Parmenides. Parmenides asks the young Socrates what he calls ideas. Socrates answers by naming unconditionally the moral ideas, the ideas of the true, the beautiful, the good, and then after a little delay he mentions some physical ones, as the ideas of man, of fire, of water; he will not allow ideas to be predicated of that which is only a formless mass, or which is a part of something else, as hair, mud and clay, but in this he is answered by Parmenides, that if he would be fully imbued with philosophy, he must not consider such things as these to be wholly despicable, but should look upon them as truly though remotely participating in the idea. Here at least the claim is asserted that no province of being is excluded from the idea, that even that which appears most accidental and irrational is yet a part of rational knowledge, in fact that every thing existing may be brought within a rational conception.