Prop. XXXVIIFrom all these considerations it is evident, that justice and injustice, sin and merit, are extrinsic ideas, and not attributes which display the nature of the mind. But I have said enough.

Prop. XXXVIII

Whatsoever disposes the human body, so as to render it capable of being affected in an increased number of ways, or of affecting external bodies in an increased number of ways, is useful to man; and is so, in proportion as the body is thereby rendered more capable of being affected or affecting other bodies in an increased number of ways; contrariwise, whatsoever renders the body less capable in this respect is hurtful to man.

Proof.--Whatsoever thus increases the capabilities of the body increases also the mind's capability of perception (II. xiv.); therefore, whatsoever thus disposes the body and thus renders it capable, is necessarily good or useful (IV. xxvi. xxvii.); and is so in proportion to the extent to which it can render the body capable; contrariwise (II. xiv., IV. xxvi. xxvii.), it is hurtful, if it renders the body in this respect less capable. Q.E.D.

Prop. XXXIX

Whatsoever brings about the preservation of the proportion of motion and rest, which the parts of the human body mutually possess, is good; contrariwise, whatsoever causes a change in such proportion is bad.

Proof.--The human body needs many other bodies for its preservation (II. Post. iv.). But that which constitutes the specific reality (forma) of a human body is, that its parts communicate their several motions one to another in a certain fixed proportion (Def. before Lemma iv. after II. xiii.). Therefore, whatsoever brings about the preservation of the proportion between motion and rest, which the parts of the human body mutually possess, preserves the specific reality of the human body, and consequently renders the human body capable of being affected in many ways and of affecting external bodies in many ways; consequently it is good (by the last Prop.). Again, whatsoever brings about a change in the aforesaid proportion causes the human body to assume another specific character, in other words (see Preface to this Part towards the end, though the point is indeed self--evident), to be destroyed, and consequently totally incapable of being affected in an increased numbers of ways; therefore it is bad. Q.E.D.

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. 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. and 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.) 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.

Proof.--Love is pleasure, accompanied by the idea of an external cause (Def. of Emotions, vi.); therefore stimulation, accompanied by the idea of an external cause is love (III. xi. note); hence love maybe excessive. Again, the strength of desire varies in proportion to the emotion from which it arises (III. xxxvii.). Now emotion may overcome all the rest of men's actions (IV. vi.); so, therefore, can desire, which arises from the same emotion, overcome all other desires, and become excessive, as we showed in the last proposition concerning stimulation.

Note.--Mirth, which I have stated to be good, can be conceived more easily than it can be observed. For the emotions, whereby we are daily assailed, are generally referred to some part of the body which is affected more than the rest; hence the emotions are generally excessive, and so fix the mind in the contemplation of one object, that it is unable to think of others; and although men, as a rule, are a prey to many emotions--and very few are found who are always assailed by one and the same--yet there are cases, where one and the same emotion remains obstinately fixed. We sometimes see men so absorbed in one object, that, although it be not present, they think they have it before them; when this is the case with a man who is not asleep, we say he is delirious or mad; nor are those persons who are inflamed with love, and who dream all night and all day about nothing but their mistress, or some woman, considered as less mad, for they are made objects of ridicule. But when a miser thinks of nothing but gain or money, or when an ambitious man thinks of nothing but glory, they are not reckoned to be mad, because they are generally harmful, and are thought worthy of being hated. But, in reality, Avarice, Ambition, Lust, &c., are species of madness, though they may not be reckoned among diseases.

Prop. XLV

Hatred can never be good.

Proof.--When we hate a man, we endeavour to destroy him (III. xxxix.), that is (IV. xxxvii.), we endeavour to do something that is bad. Therefore, &c. Q.E.D.

N.B. Here, and in what follows, I mean by hatred only hatred towards men.

Corollary I.--Envy, derision, contempt, anger, revenge, and other emotions attributable to hatred, or arising therefrom, are bad; this is evident from III. xxxix. and IV. xxxvii.

Corollary II.--Whatsoever we desire from motives of hatred is base, and in a State unjust. This also is evident from III. xxxix., and from the definitions of baseness and injustice in IV. xxxvii. note.

Note.--Between derision (which I have in Coroll. I. stated to be bad) and laughter I recognize a great difference. For laughter, as also jocularity, is merely pleasure; therefore, so long as it be not excessive, it is in itself good (IV. xli.). Assuredly nothing forbids man to enjoy himself, save grim and gloomy superstition. For why is it more lawful to satiate one's hunger and thirst than to drive away one's melancholy? I reason, and have convinced myself as follows: No deity, nor anyone else, save the envious, takes pleasure in my infirmity and discomfort, nor sets down to my virtue the tears, sobs, fear, and the like, which axe signs of infirmity of spirit; on the contrary, the greater the pleasure wherewith we are affected, the greater the perfection whereto we pass; in other words, the more must we necessarily partake of the divine nature. Therefore, to make use of what comes in our way, and to enjoy it as much as possible (not to the point of satiety, for that would not be enjoyment) is the part of a wise man. I say it is the part of a wise man to refresh and recreate himself with moderate and pleasant food and drink, and also with perfumes, with the soft beauty of growing plants, with dress, with music, with many sports, with theatres, and the like, such as every man may make use of without injury to his neighbour. For the human body is composed of very numerous parts, of diverse nature, which continually stand in need of fresh and varied nourishment, so that the whole body may be equally capable of performing all the actions, which follow from the necessity of its own nature; and, consequently, so that the mind may also be equally capable of understanding many things simultaneously. This way of life, then, agrees best with our principles, and also with general practice; therefore, if there be any question of another plan, the plan we have mentioned is the best, and in every way to be commended. There is no need for me to set forth the matter more clearly or in more detail.