What pleasure is, or what kind of thing it is, will become plainer if we take up the question again from the beginning.
You've seen this move from Aristotle throughout, and as I've mentioned, it's a very common approach of his. He brings in a lot of machinery from the Physics about what makes motion possible. By "motion" means something technical again, which he will explain to you but it's not quite the way we use the word: it's any sort of process by which change comes to be.
Seeing seems to be at any moment complete, for it does not lack anything which coming into being later will complete its form; and pleasure also seems to be of this nature. For it is a whole, and at no time can one find a pleasure whose form will be completed if the pleasure lasts longer. For this reason, too, it is not a movement. For every movement (e.g. that of building) takes time and is for the sake of an end, and is complete when it has made what it aims at. It is complete, therefore, only in the whole time or at that final moment. In their parts and during the time they occupy, all movements are incomplete, and are different in kind from the whole movement and from each other. For the fitting together of the stones is different from the fluting of the column, and these are both different from the making of the temple; and the making of the temple is complete (for it lacks nothing with a view to the end proposed), but the making of the base or of the triglyph is incomplete; for each is the making of only a part.
A point he makes about motions that are for the sake of an end is that the parts of the motion generally have to come in a certain order. The temple example here is a little opaque, but the point is easy to understand: you have to make the foundation before you can raise the walls, and the walls need to be raised before a roof can be installed. So the thing coming-to-be has an order even over and above the form you are putting the material into: the process by which it can come to be is a determined feature of reality.
They differ in kind, then, and it is not possible to find at any and every time a movement complete in form, but if at all, only in the whole time. So, too, in the case of walking and all other movements. For if locomotion is a movement from to there, it, too, has differences in kind-flying, walking, leaping, and so on.
Locomotion is more in line with how we tend to use the word "motion," but there is also here a determined set of necessary things that have to be done in order. If I want to walk to the mountaintop I first leave my house, then I cross the forest, then I climb the slopes, and only then can I step onto the summit.
(There's another crucial point about locomotion in the Physics, which is that all of these motions involve locomotion: Aristotle's understanding of the way things come to be is that you have to bring things into contact physically; he does not for example have a concept of gravity. If you want to throw a rock into the lake, you have to go to the rock, pick it up, and then throw it. Why does it fall? Natural place, as mentioned in the commentary on II.1: the rock you threw is moving to where the elemental rock belongs in the universe, which it will do if not arrested. Why does it keep moving in the air after you let go of it? His theory was that the air moved out of its way when you threw it kind of circles around behind it and continues to push it along.)
And not only so, but in walking itself there are such differences; for the whence and whither are not the same in the whole racecourse and in a part of it, nor in one part and in another, nor is it the same thing to traverse this line and that; for one traverses not only a line but one which is in a place, and this one is in a different place from that. We have discussed movement with precision in another work...
The Physics, obviously.
...but it seems that it is not complete at any and every time, but that the many movements are incomplete and different in kind, since the whence and whither give them their form. But of pleasure the form is complete at any and every time. Plainly, then, pleasure and movement must be different from each other, and pleasure must be one of the things that are whole and complete. This would seem to be the case, too, from the fact that it is not possible to move otherwise than in time, but it is possible to be pleased; for that which takes place in a moment is a whole.From these considerations it is clear, too, that these thinkers are not right in saying there is a movement or a coming into being of pleasure. For [movement or coming-to-be] cannot be ascribed to all things, but only to those that are divisible and not wholes; there is no coming into being of seeing nor of a point nor of a unit, nor is any of these a movement or coming into being; therefore there is no movement or coming into being of pleasure either; for it is a whole.
What kind of things are not divisible, even conceptually? He has named some mathematical objects that don't really exist in the world; a point is defined as having no magnitude, so there's nothing to divide. But pleasure isn't a mathematical object either, of course. It is, however, still necessarily then immaterial, for all material things can be divided and have magnitude.
Since every sense is active in relation to its object, and a sense which is in good condition acts perfectly in relation to the most beautiful of its objects (for perfect activity seems to be ideally of this nature; whether we say that it is active, or the organ in which it resides, may be assumed to be immaterial), it follows that in the case of each sense the best activity is that of the best-conditioned organ in relation to the finest of its objects. And this activity will be the most complete and pleasant. For, while there is pleasure in respect of any sense, and in respect of thought and contemplation no less, the most complete is pleasantest, and that of a well-conditioned organ in relation to the worthiest of its objects is the most complete; and the pleasure completes the activity.
Here he is continuing the analogy to sight that he opened with: sight is in the organ of the eyes, but sight as we experience it is not material. You can close one eye, but you can't divide the experience you have of seeing into physical parts.
But the pleasure does not complete it in the same way as the combination of object and sense, both good, just as health and the doctor are not in the same way the cause of a man's being healthy.
This is a concept that was important to Aristotle: 'being healthy' causes health, so the fact that all your organs are properly working is what causes the experience of being healthy. A doctor can also cause you to be healthy, sometimes, by applying surgery or other techniques; but it is not the same way of causing your health, and indeed an inferior one if you can just be healthy.
(That pleasure is produced in respect to each sense is plain; for we speak of sights and sounds as pleasant. It is also plain that it arises most of all when both the sense is at its best and it is active in reference to an object which corresponds; when both object and perceiver are of the best there will always be pleasure, since the requisite agent and patient are both present.) Pleasure completes the activity not as the corresponding permanent state does, by its immanence, but as an end which supervenes as the bloom of youth does on those in the flower of their age. So long, then, as both the intelligible or sensible object and the discriminating or contemplative faculty are as they should be, the pleasure will be involved in the activity; for when both the passive and the active factor are unchanged and are related to each other in the same way, the same result naturally follows.
So pleasure is not like building a temple; it's not a motion or a movement because it can't be divided into parts. It's also not like the way in which seeing is the purpose of the eyes, because we also experience pleasure from seeing beauty, so it's an additional sort of end -- not one that supplants sight as the purpose of the eye, the end for which eyes are made, but another sort of end. It's not weird to have two ends, because in Aristotle you have four causes, each of which can have an independence (although they often don't; formal and final cause often turn out to be the same, or efficient and material).
How, then, is it that no one is continuously pleased? Is it that we grow weary? Certainly all human beings are incapable of continuous activity. Therefore pleasure also is not continuous; for it accompanies activity. Some things delight us when they are new, but later do so less, for the same reason; for at first the mind is in a state of stimulation and intensely active about them, as people are with respect to their vision when they look hard at a thing, but afterwards our activity is not of this kind, but has grown relaxed; for which reason the pleasure also is dulled.One might think that all men desire pleasure because they all aim at life; life is an activity, and each man is active about those things and with those faculties that he loves most; e.g. the musician is active with his hearing in reference to tunes, the student with his mind in reference to theoretical questions, and so on in each case; now pleasure completes the activities, and therefore life, which they desire. It is with good reason, then, that they aim at pleasure too, since for every one it completes life, which is desirable. But whether we choose life for the sake of pleasure or pleasure for the sake of life is a question we may dismiss for the present. For they seem to be bound up together and not to admit of separation, since without activity pleasure does not arise, and every activity is completed by the attendant pleasure.
They do admit of separation conceptually, however. Note the distinction, also technical in Aristotle, between a "motion" -- which this can't be because it has to be immaterial -- and an "activity." Activities can be immaterial and indivisible; in addition to these examples, the Unmoved Movers in Aristotle's Physics VIII and Metaphysics XII are supposed to be pure activities, i.e. Forms.
A pure activity can thus be everlasting, since there's no motion to complete and no material parts to wear out. That's one reason it's a puzzle for Aristotle that our pleasure activity comes to an end after a while, which he is explaining here.
