To mix science up with philosophy is only to produce a philosophy that has lost all its ideal value and a science that has lost all its practical value. It is for my private physician to tell me whether this or that food will kill me. It is for my private philosopher to tell me whether I ought to be killed.

The Quotable Chesterton: A Topical Compilation of the Wit, Wisdom and Satire of G.K. Chesterton (ed. 1986)