onceives things which diminish or
hinder the body's power of activity, it endeavours, as far as
possible, to remember things which exclude the existence of the
first--named things.

Proof.--So long as the mind conceives anything of the kind
alluded to, the power of the mind and body is diminished or
constrained (cf. III. xii. Proof); nevertheless it will continue
to conceive it, until the mind conceives something else, which
excludes the present existence thereof (II. xvii.); that is (as
I have just shown), the power of the mind and of the body is
diminished, or constrained, until the mind conceives something
else, which excludes the existence of the former thing conceived:
therefore the mind (III. ix.), as far as it can, will endeavour
to conceive or remember the latter. Q.E.D.

Corollary.--Hence it follows that the mind shrinks from
conceiving those things, which diminish or constrain the power of
itself and of the body.

Note.--From what has been said we may clearly understand the
nature of Love and Hate. Love is nothing else but pleasure
accompanied by the idea of an external cause: Hate is nothing
else but pain accompanied by the idea of an external cause. We
further see, that he who loves necessarily endeavours to have,
and to keep present to him, the object of his love; while he who
hates endeavours to remove and destroy the object of his hatred.
But I will treat of these matters at more length hereafter.

PROP. XIV. If the mind has once been affected by two emotions at
the same time, it will, whenever it is afterwards affected by one
of these two, be also affected by the other.

Proof.--If the human body has once been affected by two bodies
at once, whenever afterwards the mind conceives one of them, it
will straightway remember the other also (II. xviii.). But the
mind's conceptions indicate rather the emotions of our body than
the nature of external bodies (II. xvi. Coroll. ii.); therefore,
if the body, and consequently the mind (III. Def. iii.) has been
once affected by two emotions at the same time, it will, whenever
it is afterwards affected by one of the two, be also affected by
the other.

PROP. XV. Anything can, accidentally, be the cause of pleasure,
pain, or desire.

Proof.--Let it be granted that the mind is simultaneously
affected by two emotions, of which one neither increases nor
diminishes its power of activity, and the other does either
increase or diminish the said power (III.