“Mathematics, synthetic unity and constitutive a priori”. Starting from the emphasis about the Kantian idea of the originary synthetic unity of apperception like the basic function on which rest the production of all synthetic judgment, in this paper I defend the idea of constitutive a priori of experience under the form of a similar synthetic principle but essentially formal, namely, the concept of transformation and group of transformations. To the same time, I try to show that Kant himself inspired, for (...) articulate his own position, on mathematics, especially on synthetic geometry. (shrink)