ecreed by common
consent what belongs to one man and what to another.

From 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