A simple physical mechanism may be a priori, in the sense of anteriority.
We should here draw a distinction between the two senses of the a priori: anteriority and superiority.
The ogive is, perhaps, very ancient; and authors dispute as to the anteriority of the Romanesque to the Gothic.
This anteriority of nature is a commonplace in philosophy: thus one says that the decrees of God have an order among themselves.
On the other hand, anteriority and posteriority exist in dimension as well as in numbers.