Timaeus
The Elements (64a)
Timaeus: regularity combined with density. In respect of the affections common to the whole body a very important point, which still remains, is the cause of the pleasures and pains attaching to the sense-affections we have been discussing; and the cause also of those affections which have become perceptible by means of the bodily parts and involve in themselves concomitant pains and pleasures. Let us, then, try to grasp the causes in connection with every perceptible and imperceptible affection in the following way,
Problems of the Soul (2) (18)
There remains the question whether the body possesses any force of its own- so that, with the incoming of the soul, it lives in some individuality-...
(18) There remains the question whether the body possesses any force of its own- so that, with the incoming of the soul, it lives in some individuality- or whether all it has is this Nature we have been speaking of, the superior principle which enters into relations with it.
Certainly the body, container of soul and of nature, cannot even in itself be as a soulless form would be: it cannot even be like air traversed by light; it must be like air storing heat: the body holding animal or vegetive life must hold also some shadow of soul; and it is body thus modified that is the seat of corporeal pains and pleasures which appear before us, the true human being, in such a way as to produce knowledge without emotion. By "us, the true human being" I mean the higher soul for, in spite of all, the modified body is not alien but attached to our nature and is a concern to us for that reason: "attached," for this is not ourselves nor yet are we free of it; it is an accessory and dependent of the human being; "we" means the master-principle; the conjoint, similarly is in its own way an "ours"; and it is because of this that we care for its pain and pleasure, in proportion as we are weak rather than strong, gripped rather than working towards detachment.
The other, the most honourable phase of our being, is what we think of as the true man and into this we are penetrating.
Pleasure and pain and the like must not be attributed to the soul alone, but to the modified body and to something intermediary between soul and body and made up of both. A unity is independent: thus body alone, a lifeless thing, can suffer no hurt- in its dissolution there is no damage to the body, but merely to its unity- and soul in similar isolation cannot even suffer dissolution, and by its very nature is immune from evil.
But when two distinct things become one in an artificial unity, there is a probable source of pain to them in the mere fact that they were inapt to partnership. This does not, of course, refer to two bodies; that is a question of one nature; and I am speaking of two natures. When one distinct nature seeks to associate itself with another, a different, order of being- the lower participating in the higher, but unable to take more than a faint trace of it- then the essential duality becomes also a unity, but a unity standing midway between what the lower was and what it cannot absorb, and therefore a troubled unity; the association is artificial and uncertain, inclining now to this side and now to that in ceaseless vacillation; and the total hovers between high and low, telling, downward bent, of misery but, directed to the above, of longing for unison.