[...] Your compositions have kept me very busy and interested. Yet from the beginning of our acquaintanceship I have felt the constraint of knowing that you expect a verdict from me which it is impossible for me to give. In the first place, how am I to get any clear notion of the thing? You know how abominably I play the piano, and that I cannot master anything by that means, unless I can form a clear conception beforehand; what I get from simple reading is not enough (compared with what I expect) to give me an idea of a composition. Now you will admit that your style is of a kind which refuses in every respect to be judged without cogent experience of the impression received from an actual performance of the work. Accordingly, I first took a look at you from the view-point of a pianist and then from that of an orchestra—an inconceivably good orchestra—to see how your work would shape. What I have managed to glean without these aids, the meagre picture which is all that I have been able to produce without them, I may not and cannot mistake for the work itself, and consequently must tell you that—you still owe it me to show me your works.—
If, however, I am to give my verdict upon what of comprehension I do believe myself to have attained in my simple way, you must be content with the following purely personal opinions.—I was struck at once by your inventiveness; your talent for this is unmistakably great and shows itself especially in the earlier composition, the Orchestral Fantasy. The thematic structure is great and comprehensive in idea and execution, and original in the Fantasy in particular, because proceeding entirely out of the subject-matter. The characterisation of the motifs is clear, yet not so decided in the Cæsar Overture as in the later Fantasy; at least, after my one laboriously achieved impression of the work, I am still unable—without being arbitrary—exactly to fit the motifs to particular subjects. [...] In both works, however, I admire your technique, in which, as regards difficulties of form both in detail and ultimate significance, you could not—in my opinion—be easily surpassed. Accordingly, I cannot but call you a Master and to my mind you can accomplish whatever you set out to do. If, as against this, I have any serious doubts (relating to matters of form), they attach to your attitude towards euphony in harmony. In this matter, I confess, my sole impression as yet is of extremely significant music played on instruments out of tune, and it is just here that I require the determinative sensuous impression of a really good performance before I can be rid of my fears. I know well from experience that even in musical representation there are subjects which cannot find expression save through harmonic motives which are bound to grate upon the ear of the musical Philistine. When, however, I perceived such in my own works, I was ever led by a definite impulse to disguise the harmonic harshness as much as possible and finally to manage so that (to my mind) they were no longer perceptible. Now I cannot get rid of the feeling that it is almost the other way round with you, that is to say, you prefer that harshness should be felt as harshness, and this strikes me most disagreeably where I see that the whole device manifests itself actually, solely in this harshness. [...]
You see, Hans, I really have been through similar stages, particularly in my earliest period as a composer when I made everything else a secondary matter till I lit upon a harmonic witticism of some kind. [...] In your case, now, I am surprised; you are certainly mistaken in yourself; you have far too much inventive power to be justified in taking serious pleasure in such paltry tricks. And it is rather a cold, hard-hearted Jew-business, is it not, when others (as is a fact) notice nothing but the curiosities in what we have to say to them, and talk to us about them as if the thing itself were nothing.—
You see what a poor opinion I have of this kind of thing and that I am convinced that my criticism of your work touches inessentials only, and not essentials. So do not take my verdict—although I will not admit that it has the value of such—as anything but most favourable to yourself. I do not recollect ever being so taken with any modern piece of music as with your Fantasy in particular, despite insufficient acquaintance.—Have you heard it? You do not tell me that.—[...]
I have found a great treasure in the works of the great philosopher Schopenhauer (deliberately ignored for thirty-five years by the professors). You must get his chief work at once, The Universe as Will and Idea [...]; after that, Parerga and Paralipomena. [...]
Source: Letters of Richard Wagner, Vol. 1, selected and ed. Wilhelm Altmann, trans. M. M. Bozman (J. M. Dent & Sons, 1927), No. 269