Note 2 — Chapter XI
Reading edition
The assertion that all perceptions (i. e. all objects of perception) are extensive quantities relates, according to Kant, to the nature of objects, while the assertion that an event must have a necessary antecedent affirms that such an antecedent must exist, but gives no clue to its specific nature. Compare "But the existence of phenomena cannot be known a priori, and although we could be led in this way to infer the fact of some existence, we should not know this existence determinately, i. e. we could not anticipate the respect in which the empirical perception of it differed from that of other existences". (B. 221, M. 134). Kant seems to think that the fact that the dynamical principles relate to the existence of objects is a sufficient justification of their name.
It needs but little reflection to see that the distinctions which Kant draws between the mathematical and the dynamical principles must break down.