Note.- The extent to which such causes can injure or be of service to the mind will be explained in the Fifth Part. But I would here remark that I consider that a body undergoes death, when the proportion of motion and rest which obtained mutually among its several parts is changed. For I do not venture to deny that a human body, while keeping the circulation of the blood and other properties, wherein the life of a body is thought to consist, may none the less be changed into another nature totally different from its own. There is no reason, which compels me to maintain that a body does not die, unless it becomes a corpse; nay, experience would seem to point to the opposite conclusion. It sometimes happens, that a man undergoes such changes, that I should hardly call him the same. As I have heard tell of a certain Spanish poet, who had been seized with sickness, and though he recovered therefrom yet remained so oblivious of his past life, that he would not believe the plays and tragedies he had written to be his own: indeed, he might have been taken for a grown-up child, if he had also forgotten his native tongue. If this instance seems incredible, what shall we say of infants? A man of ripe age deems their nature so unlike his own, that he can only be persuaded that he too has been an infant by the analogy of other men. However, I prefer to leave such questions undiscussed, lest I should give ground to the superstitious for raising new issues.
Prop. XL. Whatsoever conduces to man's social life, or causes men to live together in harmony, is useful, whereas whatsoever brings discord into a State is bad.
Proof.- For whatsoever causes men to live together in harmony also causes them to live according to reason (IV:xxxv.), and is therefore (IV:xxvi. and IV:xxvii.) good, and (for the same reason) whatsoever brings about discord is bad. Q.E.D.
Prop. XLI. Pleasure in itself is not bad but good: contrariwise, pain in itself is bad.
Proof.- Pleasure (III:xi.&Note) is emotion, whereby the body's power of activity is increased or helped; pain is emotion, whereby the body's power of activity is diminished or checked; therefore (IV:xxxviii.) pleasure in itself is good, &c. Q.E.D.
Prop. XLII. Mirth cannot be excessive, but is always good; contrariwise, Melancholy is always bad.
Proof.- Mirth (see its Def. in III:xi.Note) is pleasure. which, in so far as it is referred to the body, consists in all parts of the body being affected equally: that is (III:xi.), the body's power of activity is increased or aided in such a manner, that the several parts maintain their former proportion of motion and rest; therefore Mirth is always good (IV. xxxix.), and cannot be excessive. But Melancholy (see its Def. in the same note to III:xi.Note) is pain, which, in so far as it is referred to the body, consists in the absolute decrease or hindrance of the body's power of activity; therefore (IV:xxxviii.) it is always bad. Q.E.D.
Prop. XLIII. Stimulation may be excessive and bad; on the other hand, grief may be good, in so far as stimulation or pleasure is bad.
Proof.- Localized pleasure or stimulation (titillatio) is pleasure, which, in so far as it is referred to the body, consists in one or some of its parts being affected more than the rest (see its Definition, III:xi.Note); the power of this emotion may be sufficient to overcome other actions of the body (IV:vi.), and may remain obstinately fixed therein, thus rendering it incapable of being affected in a variety of other ways: therefore (IV:xxxviii.) it may be bad. Again, grief, which is pain, cannot as such be good (IV:xli.). But, as its force and increase is defined by the power of an external cause compared with our own (IV:v.), we can conceive infinite degrees and modes of strength in this emotion (IV:iii.); we can, therefore, conceive it as capable of restraining stimulation, and preventing its becoming excessive, and hindering the body's capabilities; thus, to this extent, it will be good. Q.E.D.
Prop. XLIV. Love and desire may be excessive.