Full Idea
For Kant the only legitimate infinity is the so-called potential infinity, not the actual infinity.
Gist of Idea
Kant only accepts potential infinity, not actual infinity
Source
report of Immanuel Kant (Critique of Pure Reason [1781]) by James Robert Brown - Philosophy of Mathematics Ch.5
Book Reference
Brown,James Robert: 'Philosophy of Mathematics' [Routledge 2002], p.65
A Reaction
This is part of what leads on the the Constructivist view of mathematics. There is a procedure for endlessly continuing, but no procedure for arriving. That seems to make good sense.