Thoughts without content are empty, intuitions without concepts are blind.

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

Immaturity is the incapacity to use one's intelligence without the guidance of another.

Metaphysics is a dark ocean without shores or lighthouse, strewn with many a philosophic wreck.

A categorical imperative would be one which represented an action as objectively necessary in itself, without reference to any other purpose.

Philosophy of science without history of science is empty; history of science without philosophy of science is blind.