Experience without theory is blind, but theory without experience is mere intellectual play.

Kant's treatment of the transcendental logic in the First Critique contains a portion, of which this quote may be an ambiguously worded paraphrase. Kant, claiming that both reason and the senses are essential to the formation of our understanding of the world, writes: "Without sensibility no object would be given to us, and without understanding none would be thought. Thoughts without content are empty, intuitions without concepts are blind (A51/B75)".