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 PLATO'S DOCTRINE OF IDEAS. 521 modern Man of Science, and Plato's account of their operations must allowance being made for modes of expression peculiar to himself and his age bear close comparison with the account of them given by a modern psychologist who should make it his business to explain how the Man of Science to-day goes to work. This Prof. Natorp sees clearly. He sees, what their lack of Psy- chology prevents the Trinity College Cambridge School and Dr. Lutoslawski from seeing clearly, or at all, that the Doctrine of Ideas has a large significance as Method of Science ; and he is very successful in expounding it as such on lines which, I am interested in noticing, are similar to those which I myself, starting from a hint of Lotze's (a hint which Prof. Natorp hardly appreciates at its true value), indicated in 1892. The dSt), so far as methodology is concerned, are points of view from which the Man of Science regards his data. They are the right points of view, and, as such, have the ' permanence ' which we nowadays ascribe to ' Laws of Nature '. They are indeed ' separate ' from phenomena ; but only so in the sense that they are the ' explanations ' as distinguished from the 'phenomena explained'. They are not 'separate' Things ; the rpiVo? aifyxuTros refutation, in the Tenth Book of the Republic and the Parmenides, disposes of the error wrongly attri- buted by Aristotle to Plato of substantiating them as separate Things. If we dismiss from our minds the prejudice raised by Aristotle's criticism we find nothing in the Dialogues of Plato to countenance the view that the Ideas, so far as they have methodo- logical significance, are ' known ' as statically existent : they are ' known ' only as dynamically existent only as performing their function of making sensibilia intelligible. It is as true of Plato's Ideas as of Kant's Categories that without sense they are empty. The Ideas, so far as their methodological significance is concerned, are nothing more than concepts-in-use the instruments by em- ploying which Human Understanding performs its work of inter- preting the world this sensible world, not another world beyond. This view of the function of Ideas in Science, Plato holds and enforces throughout the whole series of his Dialogues, and nowhere more plainly than in his earliest Dialogues, where the object is to find the eiSr/ of the Moral Virtues, that is, to explain them by exhibiting each in its special context by assigning to each its special place and use in the Social System the System of the ' Good '. Sense, and imagination, and desultory thinking ex- pressing themselves in Ehetoric present the ' Virtues ' separately, taking no account of the System in which they inhere ; dva/xvr/o-ts, described as amus Aoyioy/,ds connected thinking, stirred by Dia- lectic, works out the special context of each Virtue and the rela- tions of that context to other contexts viewed as parts, along with it, of the whole System. ' Context grasped,' ' scientific point of view taken,' ' eISo9 discovered ' these are equivalent expressions. The ?<$os is not an impression of sense passively received ; it is a product of the mind's activity an instrument constructed by the