20. Let it be granted, then, that reaction is not the contrary of action. Nevertheless, as it differs therefrom, it could not share the same genus. If both reaction and action be movements, they share the same genus, that of alteration, which is a movement, as respects quality.[279] When alteration proceeds from the being endowed with quality, is there any action, though this being remain impassible? Yes, for though impassible, it is active. It may be asked, is this being no longer active when it acts on some other object, as, for instance, by striking it, and then reacts? The answer is, that it would be active and passive simultaneously. If it be active, when it reacts--when, for instance, it rubs--why is it considered active rather than passive? Because it reacts in being rubbed while it rubs. Could we say that, because it is moved while moving, there were in it two movements? But how could there be two movements in it? Shall we assert that there is but one? In this case, how could the same movement be action and reaction simultaneously? Doubtless, it will be considered action, in so far as it proceeds from the mover; and reaction, inasmuch as it passes from the mover into the moved; and this, without ceasing to be one and the same thing. Would you say that reaction was a movement of a kind different from action? How then would the altering movement in a certain manner modify what reacts without an equal reaction in what is acting? But how (can we conceive) of reaction in that which acts on another object? Is the mere presence of the movement in the moved sufficient to constitute reaction?[280] But if, on one hand, the ("seminal) reason" of the swan whitens, and on the other hand the swan that is being born becomes white, shall we say that the swan is passive in becoming what it is his nature to be? If he becomes white even after his birth, is he still passive? If one thing increase, and another thing be increased, will we admit that the thing that increases reacts? Will we rather attribute reaction to the thing qualified? If one thing be embellished, and another thing embellishes it, could we say that the embellished thing reacts?[281] If however, the embellishing thing decreases, and, like tin, tarnishes, or on the contrary, like copper, takes on polish; shall we say that the tin acts, and the copper reacts (that is, "suffers")? Besides, it would be impossible to say that that which learns is passive (suffering)? Would this be because the action of him who acts passes into him? But how could there be any reaction ("suffering") since there is nothing there but an act? This action, no doubt, is not a reaction ("suffering"); but he who receives it is passive, because he participates in passivity. Indeed, from the fact that the learner does not himself act, it does not necessarily result that he is passive; for learning is not being struck, but grasping and discerning, as takes place with the process of vision.