8. The nature of species, as formed by us. And that the species of
things to us are nothing but the ranking them under distinct names,
according to the complex ideas in us, and not according to precise,
distinct, real essences in them, is plain from hence:- That we find
many of the individuals that are ranked into one sort, called by one
common name, and so received as being of one species, have yet
qualities, depending on their real constitutions, as far different one
from another as from others from which they are accounted to differ
specifically. This, as it is easy to be observed by all who have to do
with natural bodies, so chemists especially are often, by sad
experience, convinced of it, when they, sometimes in vain, seek for
the same qualities in one parcel of sulphur, antimony, or vitriol,
which they have found in others. For, though they are bodies of the
same species, having the same nominal essence, under the same name,
yet do they often, upon severe ways of examination, betray qualities
so different one from another, as to frustrate the expectation and
labour of very wary chemists. But if things were distinguished into
species, according to their real essences, it would be as impossible
to find different properties in any two individual substances of the
same species, as it is to find different properties in two circles, or
two equilateral triangles.
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