— 330 —
Principium Individuationis.       §3. From what has been said, ’tis easy to discover, what is so
much enquired after, the principium Individuationis, and that ’tis plain
is Existence it self, which determines a Being of any sort to a
particular time and place incommunicable to two Beings of the
same kind. This though it seems easier to conceive in simple
Substances or Modes; yet when reflected on, is not more difficult in
compounded ones, if care be taken to what it is applied; v.g. Let
us suppose an Atom, i.e. a continued body under one immutable
Superficies, existing in a determined time and place:’tis evident,
that, considered in any instant of its Existence, it is, in that instant,
the same with it self. For being, at that instant, what it is, and
nothing else, it is the same, and so must continue, as long as its
Existence is continued: for so long it will be the same, and no other.
In like manner, if two or more Atoms be joined together into the
same Mass, every one of those Atoms will be the same, by the fore-
going Rule: And whilst they exist united together, the Mass,
consisting of the same Atoms, must be the same Mass, or the same
Body, let the parts be never so differently jumbled: But if one of
these Atoms be taken away, or one new one added, it is no longer
the same Mass, or the same Body. In the state of living Creatures,
their Identity depends not on a Mass of the same Particles; but
on something else. For in them the variation of great parcels of
Matter alters not the Identity: An Oak, growing from a Plant to
a great Tree, and then lopp’d, is still the same Oak: And a Colt
grown up to a Horse, sometimes fat, sometimes lean, is all the while
the same Horse: though, in both these Cases, there may be a
manifest change of the parts: So that truly they are not either of
them the same Masses of Matter, though they be truly one of them
the same Oak, and the other the same Horse. The reason whereof is,
that in these two cases of a Mass of Matter, and a living Body,
Identity is not applied to the same thing.
Locke Hum II, 27, §3, p. 330