The word "affection" is spoken of in two ways, for it is what leads either to destruction or to completion. Thus it is said that a piece of wood is affected by fire, meaning that it is brought to destruction; it is also said that sensations are affected by sensible things,[1] meaning that they are fulfilled and are transformed from a potentiality to an actuality.
And something passes from the affections of the body to the soul, for the soul sympathizes with a body in pain[2] and rejoices with one that is cheerful. Nobody is unaware that the body, when disposed one way or another, interferes with the soul. This would not occur if a certain sympathy[3] did not pass from the condition of the body to the soul, just as the faculty of memory is affected when the rear chamber of the brain is affected.
On affections: the parts of the soul are the five sense-organs, the part that relates to speech, and the thinking part, which is thought.[4] Distortion comes to thought from falsehoods and, due to such a distortion, many affections arise which are causes of instability. The affection itself is a movement of the soul which is irrational and contrary to nature, or an impulse which is excessive.[5] The most generic division of affections is into four: pain, fear, appetite, pleasure. It seems to be[6] that the affections are judgments, for greed is a supposition that money is something fine or noble.[7] And the same thing occurs in the case of drunkenness, intemperance and the others. And pain[8] is an irrational contraction and its types are piety, envy, rivalry, resentment, distress, anxiety, folly, agony, confusion. Pity is the type of pain felt for someone suffering undeservedly; envy is pain over someone else's good fortunes; rivalry is a pain that comes from the fact that another person has what one also has oneself; distress is an oppressive pain; anxiety is a disabling pain that makes it difficult to act; folly is a persistent and growing pain that arises in deliberations; agony is an intense pain; confusion is an irrational and tormenting pain which prevents one from perceiving one's circumstances.
Immortality is an affection of life or some kind of accident: That immortality is an affection of life or some kind of accident will be proven on the ground of the hypothesis that the immortal comes to be from the mortal. For the mortal will not be immortal because of participation in another life but because of some kind of accident and affection. For the same life, in being affected, is immortality. But if life becomes immortality as cause of affection, life would be an affection of immortality. Therefore, if what has been affected is not a type of a particular affection (for the affection of what has been affected is a certain coincidence, i.e. an accident, but not a form), life would not be a type of immortality. For neither is the body a type of sweetness nor the soul a type of pleasure or pain.
This topic has also been treated in the [entry] "immortal", but more broadly there.[9]