granted at least that its going from one thought to another implies some
reason of affinity. If I suppose that in a certain moment the soul of
Caesar sees a tree with leaves and blossoms, I can conceive that it does
immediately desire to see one that has only leaves, and then one that has
only blossoms, and that it will thus successively produce several images
arising from one another; but one cannot conceive the odd change of
thoughts, which have no affinity with, but are even contrary to, one
another, and which are so common in men's souls. One cannot apprehend how
God could place in the soul of Julius Caesar the principle of what I am
going to say. He was without doubt pricked with a pin more than once, when
he was sucking; and therefore according to M. Leibniz's hypothesis which I
am here considering, his soul must have produced in itself a sense of pain
immediately after the pleasant sensations of the sweetness of the milk,
which it had enjoyed for the space of two or three minutes. By what springs
was it determined to interrupt its pleasures and to give itself all of a
sudden a sense of pain, without receiving any intimation of preparing
itself to change, and without any new alteration in its substance? If you
run over the life of that Roman emperor, every page will afford you matter
for a stronger objection than this is.

'VII. The thing would be less incomprehensible if it were supposed that the
soul of man is not one spirit but rather a multitude of spirits, each of
which has its functions, that begin and end precisely as the changes made
in a human body require. By virtue of this supposition it should be said
that something analogous to a great number of wheels and springs, or of
matters that ferment, disposed according to the changes of our machine,
awakens or lulls asleep for a certain time the action of each of those
spirits. But then the soul of man would be no longer a single substance[44]
but an _ens per aggregationem_, a collection and heap of substances just
like all material beings. We are here in quest of a single being, which