On The Soul   

two right angles to know the essential nature of the straight and

the curved or of the line and the plane) but also conversely, for

the knowledge of the essential nature of a substance is largely

promoted by an acquaintance with its properties: for, when we are able

to give an account conformable to experience of all or most of the

properties of a substance, we shall be in the most favourable position

to say something worth saying about the essential nature of that

subject; in all demonstration a definition of the essence is

required as a starting-point, so that definitions which do not

enable us to discover the derived properties, or which fail to

facilitate even a conjecture about them, must obviously, one and

all, be dialectical and futile.

A further problem presented by the affections of soul is this: are

they all affections of the complex of body and soul, or is there any

one among them peculiar to the soul by itself? To determine this is

indispensable but difficult. If we consider the majority of them,

there seems to be no case in which the soul can act or be acted upon

without involving the body; e.g. anger, courage, appetite, and

sensation generally. Thinking seems the most probable exception; but

if this too proves to be a form of imagination or to be impossible

without imagination, it too requires a body as a condition of its

existence. If there is any way of acting or being acted upon proper to

soul, soul will be capable of separate existence; if there is none,

its separate existence is impossible. In the latter case, it will be

like what is straight, which has many properties arising from the

straightness in it, e.g. that of touching a bronze sphere at a

point, though straightness divorced from the other constituents of the

straight thing cannot touch it in this way; it cannot be so divorced

at all, since it is always found in a body. It therefore seems that

all the affections of soul involve a body-passion, gentleness, fear,

pity, courage, joy, loving, and hating; in all these there is a

concurrent affection of the body. In support of this we may point to