BOOK I PART II
to approach each other, and to unite in such a
manner that the body, which results from their
union, is no more extended than either of them;
it is this we must mean when we talk of pen-
etration. But it is evident this penetration is
nothing but the annihilation of one of these
bodies, and the preservation of the other, with-
out our being able to distinguish particularly
which is preserved and which annihilated. Be-
fore the approach we have the idea of two bod-
ies. After it we have the idea only of one. It is
impossible for the mind to preserve any notion
of difference betwixt two bodies of the same
nature existing in the same place at the same
time.
Taking then penetration in this sense, for the
annihilation of one body upon its approach
to another, I ask any one, if he sees a neces-