Arguments for and against this view flashed through my mind, and I thought involuntarily of a great master of music who, when he was asked: "What is Genius?" answered: "A genius is one to whom ideas occur." This parallel might be carried still further, for I have repeatedly heard Einstein call "ideas" what we would regard as wonderful thoughts. Does not the philosopher Fritz Mauthner speak of the discovery of gravitation as being an "aperçu" of Newton; yes, in the sense of _aperçus_ as applied in ancient Greek philosophy, and which included almost everything that was left by Pythagoras, Heraclitus, etc., as a token of their genius. On the other hand, we are all possessed of the desire to differentiate clearly between an idea and a creative act of thought, as occurs in Grillparzer's aphorism: "An idea is not a thought; a thought knows its bounds, whereas the idea leaps over them and succeeds in accomplishing nothing!" Here, then, we must revise our view. We know, for example, how much Einstein's "ideas," felt by him to be such and named so accordingly, accomplished. Let us hear how he characterizes in a few words his own "idea" which shook the world: "The underlying thought of relativity," he said, in connexion with this question, "is that there is physically no unique (specially favoured) state of motion. Or, more exactly, among all states of motion there is none that is favoured in the sense that, in contradistinction to the others, it may be said to be a state of rest. Rest and Motion are not only by formal definition but also by their intrinsic physical meaning _relative conceptions_." "Well, then," I interposed, "surely this was a creative act! This first flashed across _your_ mind, Professor; it represents your discovery, so that we may well let the word retain the meaning usually associated with it!" "By no means," answered Einstein, "for it is not true that this fundamental principle occurred to me as the primary thought. If this had been so perhaps it would be justifiable to call it a "discovery." But the suddenness with which you assume it to have occurred to me must be denied. Actually, I was lead to it by _steps_ arising from the _individual_ laws derived from experience." Einstein supplemented this by emphasizing the conception "invention," and ascribed a considerable importance to it: "Invention occurs here as a constructive act. This does not, therefore, constitute what is essentially original in the matter, but the creation of a method of thought to arrive at a logically coherent system ... the really valuable factor is _intuition_!"