James’s high opinion of Bergson’s work is clear from the letter that he wrote to Bergson on June 13, 1907 (The Letters of William James, Edited by his son Henry James; Page 290-294). Here’s an excerpt from James’s letter:
O my Bergson, you are a magician, and your book is a marvel, a real wonder in the history of philosophy, making, if I mistake not, an entirely new era in respect of matter, but unlike the works of genius of the “transcendentalist” movement (which are so obscurely and abominably and inaccessibly written), a pure classic in point of form. You may be amused at the comparison, but in finishing it I found the same after-taste remaining as after finishing “Madame Bovary,” such a flavor of persistent euphony, as of a rich river that never foamed or ran thin, but steadily and firmly proceeded with its banks full to the brim. Then the aptness of your illustrations, that never scratch or stand out at right angles, but invariably simplify the thought and help to pour it along! Oh, indeed you are a magician! And if your next book proves to be as great an advance on this one as this is on its two predecessors, your name will surely go down as one of the great creative names in philosophy.
There! have I praised you enough? What every genuine philosopher (every genuine man, in fact) craves most is praise — although the philosophers generally call it “recognition”! If you want still more praise, let me know, and I will send it, for my features have been on a broad smile from the first page to the last, at the chain of felicities that never stopped. I feel rejuvenated.
As to the content of it, I am not in a mood at present to make any definite reaction. There is so much that is absolutely new that it will take a long time for your contemporaries to assimilate it, and I imagine that much of the development of detail will have to be performed by younger men whom your ideas will stimulate to coruscate in manners unexpected by yourself. To me at present the vital achievement of the book is that it inflicts an irrecoverable death-wound upon Intellectualism. It can never resuscitate! But it will die hard, for all the inertia of the past is in it, and the spirit of professionalism and pedantry as well as the aesthetic-intellectual delight of dealing with categories logically distinct yet logically connected, will rally for a desperate defense. The élan vital, all contentless and vague as you are obliged to leave it, will be an easy substitute to make fun of. But the beast has its death-wound now, and the manner in which you have inflicted it (interval versus temps d'arrêt, etc.) is masterly in the extreme. I don’t know why this later redaction of your critique of the mathematics of movement has seemed to me so much more telling than the early statement — I suppose it is because of the wider use made of the principle in the book.In this letter, James is talking about Bergson's new book Creative Evolution. He goes on to inform Bergson of his own book Pragmatism: “You will be receiving my own little “pragmatism” book simultaneously with this letter. How jejune and inconsiderable it seems in comparison with your great system! it seems in comparison with your great system! But it is so congruent with parts of your system, fits so well into interstices thereof, that you will easily understand why I am so enthusiastic. I feel that at bottom we are fighting the same fight, you a commander, I in the ranks.”