What is the character of the Nous, according to Anaxagoras? Is it, in the first place, really conceived as purely non-material and incorporeal? Aristotle, who was in a position to know more of the matter than any modern scholar, clearly implies in his criticism that the Nous of Anaxagoras is an incorporeal principle, and he has been followed in this by the majority of the best modern writers, such as Zeller and Erdmann. But the opposite view has been maintained, by Grote, for example, and more recently by Professor Burnet, who thinks that Anaxagoras conceived the Nous as a material and physical force. [Footnote 8] As the matter is of fundamental importance, I will mention the chief arguments upon which Professor Burnet rests his case. In the first place Anaxagoras described the Nous as the "thinnest and purest of all things." He also said that it was "unmixed," that it had in it no mixture of anything besides itself. Professor Burnet argues that such words as "thin" and "unmixed" would be meaningless in connection with an incorporeal principle. Only material things can properly be described as thin, pure, and unmixed. Secondly, Professor Burnet thinks that it is quite certain that the Nous occupies space, for Anaxagoras speaks of greater and smaller portions of it. Greater and smaller are spatial relations. Hence the Nous occupies space, and that which occupies space is material. But surely these are very inconclusive arguments. In the first place as regards the use of the words "thin" and "unmixed." It is true that these terms express primarily physical qualities. But, as I pointed out in {99} the first chapter, almost all words by which we seek to express incorporeal ideas have originally a physical signification. And if Anaxagoras is to be called a materialist because he described the Nous as thin, then we must also plead guilty to materialism if we say that the thought of Plato is "luminous," or that the mind of Aristotle is "clear." The fact is that all philosophy labours under the difficulty of having to express non-sensuous thought in language which has been evolved for the purpose of expressing sensuous ideas. There is no philosophy in the world, even up to the present day, in which expressions could not be found in plenty which are based upon the use of physical analogies to express entirely non-physical ideas. Then as regards the Nous occupying space, it is not true that greater and smaller are necessarily spatial relations. They are also qualitative relations of degree. I say that the mind of Plato is greater than the mind of Callias. Am I to be called a materialist? Am I to be supposed to mean that Plato's mind occupies more space than that of Callias? And it is certainly in this way that Anaxagoras uses the terms. "All Nous," he says, "is alike, both the greater and the smaller." He means thereby that the world-forming mind (the greater) is identical in character with the mind of man (the smaller). For