From Stravinsky’s Poetics of Music in the form of six lessons (1948), translated by Arthur Knodel and Ingolf Dahl:
For myself, I have always considered that in general it is more satisfactory to proceed by similarity rather than by contrast. Music thus gains strength in the measure that it does not succumb to the seductions of variety. What it loses in questionable riches it gains in true solidity.
Contrast produces an immediate effect. Similarity satisfies us only in the long run. Contrast is an element of variety, but it divides our attention. Similarity is born of a striving for unity. The need to seek variety is perfectly legitimate, but we should not forget that the One precedes the Many. Moreover, the coexistence of both is constantly necessary, and all the problems of art, like all possible problems for that matter, including the problem of knowledge and of Being, revolve ineluctably about this question, with Parmenides on one side denying the possibility of the Many, and Heraclitus on the other denying the existence of the One. Mere common sense, as well as supreme wisdom, invite us to affirm both the one and the other. All the same, the best attitude for a composer in this case will be the attitude of a man who is conscious of the hierarchy of values and who must make a choice. Variety is valid only as a means of attaining similarity. Variety surrounds me on every hand. So I need not fear that I shall be lacking in it, since I am constantly confronted by it. Contrast is everywhere. One has only to take note of it. Similarity is hidden; it must be sought out, and it is found only after the most exhaustive efforts. When variety tempts me, I am uneasy about the facile solutions it offers me. Similarity, on the other hand, poses more difficult problems but also offers results that are more solid and hence more valuable to me.