The extent to which the scientific method has yielded to analysis in recent years serves only to emphasize by contrast the presence within that method of an irrational element. For it is becoming increasingly evident that whatever one may say of the logical and psychological character of the pre-inductive operations, of the formal processes involved in deducing the consequences of a given theory, of the technique of experimental corroboration, and of certain other aspects of the scientific method, there is one phase of the movement which remains a surd. This is the act of the creative imagination through which hypotheses and theories are called into being. Its mysterious character is exhibited in the terminology which is employed in describing it, in the variety and inconstancy of the conditions which give rise to it, in the apparent impossibility of controlling it, and in the impossibility of recognizing completely the adequacy of its results when it does occur. It is variously described as an act of intuition, mystic revelation, divine insight, a flash of understanding; it arises out of the greatest variety of conditions: acute and prolonged attention to the data in the confinement of the laboratory, or the complete relaxation of a walk in the country, or the intense mental effort upon a problem in a wholly unrelated field; it forbids direction, in fact it seems to arise most readily when the element of effort and control is conspicuously absent; it cannot even be certainly identified, for many supposed acts of discovery prove later to have produced only groundless fancies and absurd creations of the unguided imagination.