15. Of repugnancy to co-exist, our knowledge is larger. As to the
incompatibility or repugnancy to coexistence, we may know that any
subject may have of each sort of primary qualities but one
particular at once: v.g. each particular extension, figure, number
of parts, motion, excludes all other of each kind. The like also is
certain of all sensible ideas peculiar to each sense; for whatever
of each kind is present in any subject, excludes all other of that
sort: v.g. no one subject can have two smells or two colours at the
same time. To this, perhaps will be said, Has not an opal, or the
infusion of lignum nephriticum, two colours at the same time? To which
I answer, that these bodies, to eyes differently placed, may at the
same time afford different colours: but I take liberty also to say, to
eyes differently placed, it is different parts of the object that
reflect the particles of light: and therefore it is not the same
part of the object, and so not the very same subject, which at the
same time appears both yellow and azure. For, it is as impossible that
the very same particle of any body should at the same time differently
modify or reflect the rays of light, as that it should have two
different figures and textures at the same time.
16. Our knowledge of the co-existence of powers in bodies extends
but a very little way.
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