: Let us duly consider its uncertainty and endless contrarieties, even in subjects of common life and practice: Let the errors and deceits of our very senses be set before us; the insuperable difficulties which attend first principles in all systems; the contradictions which adhere to the very ideas of matter, cause and effect, extension, space, time, motion; and in a word, quantity of all kinds, the object of the only science that can fairly pretend to any certainty or evidence.