portion of the Natural Law. For the matter of the negative precepts of
that law is, as we have seen, something bad in itself and repugnant to
human nature, and accordingly forbidden by God: while the matter of
the positive precepts is something good and necessary to man,
commanded by God. If God were to take off His command, or prohibition,
the intrinsic exigency, or intolerableness, of the thing to man would
still remain, being as inseparable from humanity as certain
mathematical properties from a triangle. Pride is not made for man,
nor fornication, nor lying, nor polygamy [Footnote 14]: human nature
would cry out against them, even were the Almighty in a particular
instance to withdraw His prohibition. What would be the use, then, of
any such withdrawal? It would not make the evil thing good. An evil
thing it would still remain, unnatural, irrational, and as such,
displeasing to God, the Supreme Reason. The man would not be free to
do the thing, even though God did not forbid it. It appears,
therefore, that the Divine prohibition, and similarly the Divine
command, which we have proved (c. vi., s. ii., nn. 10, 11, p. 121) to
be necessarily imposed in matters of natural evil and of naturally
imperative good, is imposed as a hard and fast line, so long as the
intrinsic good or evil remains the same.

[Footnote 14: There is a theological difficulty about the polygamy of
the patriarchs, which will be touched on in _Natural Law_, c. vi., s.
ii., n. 4. p. 272.]

4. There is, therefore, no room for Evolution in Ethics and Natural
Law any more than in Geometry. One variety of geometrical
construction, or of moral action, may succeed another; but the truths
of the science, by which those varieties are judged, change not. There
is indeed this peculiarity about morality, distinguishing it from art,