Full Idea
Although all these principles .....are generated in the mind completely a priori, they would still not signify anything at all if we could not always exhibit their significance in appearances (empirical objects).
Gist of Idea
Maths is a priori, but without its relation to empirical objects it is meaningless
Source
Immanuel Kant (Critique of Pure Reason [1781], B299/A240)
Book Reference
Kant,Immanuel: 'Critique of Pure Reason', ed/tr. Guyer,P /Wood,A W [CUO 1998], p.341
A Reaction
This is the subtle Kantian move that we all have to take seriously when we try to assert 'realism' about anything. Our drive for meaning creates our world for us?