16. Morality capable of demonstration.
Upon this ground it is that I am bold to think that morality is capable of
demonstration, as well as mathematics: since the precise real essence of the things moral words stand for may be
perfectly known, and so the congruity and incongruity of the things themselves be certainly discovered; in which
consists perfect knowledge. Nor let any one object, that the names of substances are often to be made use of in
morality, as well as those of modes, from which will arise obscurity. For, as to substances, when concerned in
moral discourses, their divers natures are not so much inquired into as supposed: v.g. when we say that man is
subject to law, we mean nothing by man but a corporeal rational creature: what the real essence or other qualities
of that creature are in this case is no way considered. And, therefore, whether a child or changeling be a man, in a
physical sense, may amongst the naturalists be as disputable as it will, it concerns not at all the moral man, as I
may call him, which is this immovable, unchangeable idea, a corporeal rational being. For, were there a monkey,
or any other creature, to be found that had the use of reason to such a degree, as to be able to understand general
signs, and to deduce consequences about general ideas, he would no doubt be subject to law, and in that sense be a
man, how much soever he differed in shape from others of that name. The names of substances, if they be used in
them as they should, can no more disturb moral than they do mathematical discourses; where, if the
mathematician speaks of a cube or globe of gold, or of any other body, he has his clear, settled idea, which varies
not, though it may by mistake be applied to a particular body to which it belongs not.
