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Powers a great part of our complex Ideas of Substances.       §7. For he has the perfectest Idea of any of the particular sorts of
Substance, who has gathered, and put together, most of those simple
Ideas, which do exist in it, among which are to be reckoned its
active Powers, and passive Capacities; which though not simple
Ideas, yet, in this respect, for brevity’s sake, may conveniently
enough be reckoned amongst them. Thus the power of drawing
Iron, is one of the Ideas of the Complex one of that substance we call
a Load-stone, and a Power to be so drawn is a part of the Complex
one we call Iron; which Powers pass for inherent Qualities in those
Subjects. Because every Substance being as apt, by the Powers we
observe in it, to change some sensible Qualities in other Subjects,
as it is to produce in us those simple Ideas, which we receive
immediately from it, does, by those new sensible Qualities intro-
duced into other Subjects, discover to us those Powers, which do
thereby mediately affect our Senses, as regularly, as its sensible
Qualities do it immediately, v.g. we immediately by our Senses
perceive in Fire its Heat and Colour; which are, if rightly considered,
nothing but Powers in it, to produce those Ideas in us: We also by
our Senses perceive the colour and brittleness of Charcoal, whereby
we come by the Knowledge of another Power in Fire, which it has
to change the colour and consistency of Wood. By the former Fire
immediately, by the latter it mediately discovers to us these several
Powers, which therefore we look upon to be a part of the Qualities
of Fire, and so make them a part of the complex Ideas of it. For all
those Powers, that we take Cognizance of, terminating only in the
alteration of some sensible Qualities, in those Subjects, on which
they operate, and so making them exhibit to us new sensible Ideas,
therefore it is, that I have reckoned these Powers amongst the simple
Ideas, which make the complex ones of the sorts of Substances; though
these Powers, considered in themselves, are truly complex Ideas.
And in this looser sence, I crave leave to be understood, when I
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name any of these Potentialities amongst the simple Ideas, which we
recollect in our Minds, when we think of particular Substances. For
the Powers that are severally in them, are necessary to be considered,
if we will have true distinct Notions of the several sorts of Sub-
stances.
Locke Hum II, 23, §7, pp. 299-300