of Substances contain not ideas of their
real Constitutions, we can make but few general Propositions concerning
them.

This is evident, the abstract complex ideas of substances, for which
their general names stand, not comprehending their real constitutions,
can afford us very little universal certainty. Because our ideas of them
are not made up of that on which those qualities we observe in them, and
would inform ourselves about, do depend, or with which they have any
certain connexion: v.g. let the ideas to which we give the name MAN be,
as it commonly is, a body of the ordinary shape, with sense, voluntary
motion, and reason joined to it. This being the abstract idea, and
consequently the essence of OUR species, man, we can make but very few
general certain propositions concerning man, standing for such an idea.
Because, not knowing the real constitution on which sensation, power of
motion, and reasoning, with that peculiar shape, depend, and whereby
they are united together in the same subject, there are very few other
qualities with which we can perceive them to have a necessary connexion:
and therefore we cannot with certainty affirm: That all men sleep by
intervals; That no man can be nourished by wood or stones; That all men
will be poisoned by hemlock: because these ideas have no connexion nor
repugnancy with this our nominal essence of man, with this abstract idea
that name stands for. We must, in these and the like, appeal to trial in
particular subjects, which can reach but a little way. We must content
ourselves with probability in the rest: but can have no general
certainty, whilst our specific idea of man contains not that real
constitution which is the root wherein all his inseparable qualities are
united, and from whence they flow. Whilst our idea the word MAN stands
for is only an imperfect collection of some sensible qualities and
powers in him, there is no discernible connexion or repugnance between
our specific idea, and the operation of either the parts of hemlock or
stones upon his constitution. There are animals that safely eat hemlock,
and others that are nourished by wood and stones: but as long as we want
ideas of those real constitutions of different sorts of animals whereon
these and the like qualities and powers depend, we must not hope to
reach certainty in universal propositions concerning them. Those few
ideas only which have a discernible connexion with our nominal essence,
or any part