— 417 —
Supposition that Species are distinguished by their real Essences useless.       §17. Concerning the real Essences of corporeal Substances, (to
mention those only,) there are, if I mistake not, two Opinions. The
— 418 —
one is of those, who using the Word Essence, for they know not what,
suppose a certain number of those Essences, according to which, all
natural things are made, and wherein they do exactly every one of
them partake, and so become of this or that Species. The other, and
more rational Opinion, is of those, who look on all natural Things
to have a real, but unknown Constitution of their insensible Parts,
from which flow those sensible Qualities, which serve us to dis-
tinguish them one from another, according as we have Occasion to
rank them into sorts, under common Denominations. The former of
these Opinions, which supposes these Essences, as a certain number of
Forms or Molds, wherein all natural Things, that exist, are cast,
and do equally partake, has, I imagine, very much perplexed the
Knowledge of natural Things. The frequent Productions of Mon-
sters, in all the Species of Animals, and of Changelings, and other
strange Issues of humane Birth, carry with them difficulties, not
possible to consist with this Hypothesis: Since it is as impossible, that
two Things, partaking exactly of the same real Essence, should have
different Properties, as that two Figures partaking in the same real
Essence of a Circle, should have different Properties. But were there
no other reason against it, yet the supposition of Essences, that cannot be
known; and the making them nevertheless to be that, which dis-
tinguishes the Species of Things, is so wholly useless, and unservice-
able to any part of our Knowledge, that that alone were sufficient,
to make us lay it by; and content our selves with such Essences of the
Sorts or Species of Things, as come within the reach of our Know-
ledge: which, when seriously considered, will be found, as I have
said, to be nothing else, but those abstract complex Ideas, to which
we have annexed distinct general Names.
Locke Hum III, 3, §17, pp. 417-418