If in the course of the five and twenty centuries during which works of high art have been produced, some of them had been executed with the assistance of a psychological impulse directed independently of the will, there would certainly have been references to the phenomenon by the artists concerned, or the very numerous art historians, but without a known exception, all the great artists who have left any record of the cause of their success, or whose views on the subject are to be gained by indirect references, have attributed this success to hard study, or manual industry, or both together. We know little of the opinion of the ancient Greeks on the matter, but the few anecdotes we have, indicate that their artists were very practical men indeed, and hardly likely to expect mysterious psychological influences to help them in their work. So with the Romans, and it is noticeable that the key to the production of beauty in poetry, in the opinion of Virgil and Horace, is careful preparation and unlimited revision. This appears to be the view of some modern poets, and if Dante, Shakespeare, and Milton, had experienced visionary inspiration, we should surely have heard of it. Fortunately some of the most eminent painters of modern times have expressed themselves definitely upon the point. Lionardo observed that the painter arrives at perfection by manual operation; and Michelangelo asserted that Raphael acquired his excellence by study and application. Rubens praised his brushes, by which he meant his acquired facility, as the instruments of his fortune; and Nicholas Poussin attributed his success to the fact that he neglected nothing, referring of course to his studies. According to his biographers, the triumphs of Claude were due to his untiring industry, while Reynolds held that nothing is denied to well directed labour. And so with many others down to Turner, whose secret according to Ruskin, was sincerity and toil. It would seem to be possible for an artist to work himself into a condition of emotional excitement,[7] either involuntarily when a great thought comes to him, or voluntarily when he seeks ideas wherewith to execute a brilliant conception; and it is comprehensible that when in this condition, which is practically an extreme concentration of his mental energy upon the purpose in hand, images or other æsthetic suggestions suitable for his work may present themselves to his mind. These he might regard as the result of inspiration, but in reality they would be the product of a trained imagination operating under advantageous conditions.