25. Of what do composition (blending, or mixture) and decomposition consist? Do they constitute other kinds of movement than those already noticed, generation and destruction, growth and decrease, movement of displacement and alteration? Shall composition and decomposition be reduced to some one of these kinds of motion, or shall we look at this process inversely? If composition consist in approximating one thing to another, and in joining them together; and if, on the other hand, decomposition consist in separating the things which were joined, we have here only two movements of displacement, a uniting, and a separating one. We should be able to reduce composition and decomposition to one of the above recognized kinds of motion, if we were to acknowledge that this composition was mingling,[427] combination, fusion, and union--a union which consists in two things uniting, and not in being already united. Indeed, composition includes first the movement of displacement, and then an alteration; just as, in increase, there was first the movement of displacement, and then movement in the kind of the quality.[428] Likewise, here there is first the movement of displacement, then the composition or decomposition, according as things approximate or separate.[429] Often also decomposition is accompanied or followed by a movement of displacement, but the things which separate undergo a modification different from the movement of displacement; similarly, composition is a modification which follows the movement of displacement, but which has a different nature. COMPOSITION AND DECOMPOSITION ARE NOT ALTERATIONS.