John Locke on the Limits of Human ReasonAn Essay Concerning Human Understanding, ed. Alexander Fraser (New York: Dover, 1959; orig. 1689), p. 31.
Men, extending their inquiries beyond their capacities, and letting their thought wander into those depths where they can find no sure footing, it is no wonder that they raise questions and multiply disputes, which, never coming to any clear resolution, are proper only to continue and increase their doubts, and to confirm them at last in perfect skepticism. Whereas were the capacities of our understandings well considered, the extent of our knowledge once discovered, and the horizon found which sets the bounds between the enlightened and dark parts of things; between what is and what is not comprehensible by us, men would perhaps with less scruple acquiesce in the avowed ignorance of the one, and employ their thoughts and discourse with more advantage and satisfaction in the other.