elements in the object apprehended (i. e. the manifold of phenomena)
with the apprehensions of them, we approach the vindication itself
with the expectation that he will identify a causal rule, which
consists in a necessity in the succession of objects, viz. of events
in nature, with the necessity in the succession of our apprehensions
of them. This expectation turns out justified. The following passage
adequately expresses the vindication:

"Let us now proceed to our task. That something happens, i. e. that
something or some state comes to be which before was not, cannot be
empirically perceived, unless a phenomenon precedes, which does not
contain in itself this state; for a reality which follows upon an
empty time, and therefore a coming into existence preceded by no state
of things, can just as little be apprehended as empty time itself.
Every apprehension of an event is therefore a perception which follows
upon another perception. But because this is the case with all
synthesis of apprehension, as I have shown above[33] in the phenomenon
of a house, the apprehension of an event is thereby not yet
distinguished from other apprehensions. But I notice also, that if in
a phenomenon which contains an event, I call the preceding state of my
perception A, and the following state B, B can only follow A in
apprehension, while the perception A cannot follow B but can only
precede it. For example, I see a ship float down a stream. My
perception of its place lower down follows upon my perception of its
place higher up the course of the river, and it is impossible that in
the apprehension of this phenomenon the vessel should be perceived
first below and afterwards higher up the stream. Here, therefore, the
order in the sequence of perceptions in apprehension is determined,
and apprehension is bound to this order. In the former example of a
house, my perceptions in apprehension could begin at the roof and end
at the foundation, or begin below and end above; in the same way they
could apprehend the manifold of the empirical perception from left to
right, or from right to left. Accordingly, in the series of these
perceptions, there was no determined order, which necessitated my
beginning at a certain point, in order to combine the manifold
empirically. But this rule is always to be found in the perception of
that which happens, and it makes the order of the successive
perceptions (in the apprehension of this phenomenon) _necessary