[samvega_]

Kant's critiqe of pure reason was what the title suggests actually, he also argued that logic (i.e pure reason), cannot hammer out ethics (what one ought to do) nor metaphysics (what ultimately is). It's only practical reason which can determine morality, i.e. his point of departure for his ethical theory is the acting being, not pure logic.

[masswerk]

And you could even say that Wittgenstein took a somewhat similar route, when he shifted his interest from the unanswerable riddle of existence and its implications to the exploration of meaningful existence as a human being, which is inevitably involved in a social process. (Mind that this is not suggesting any substantial similarities beyond this.)