Newton's Rules of Reasoning in Natural Philosophy

RULE I   We are to admit no more causes of natural things, than such as are both true and sufficient to explain their appearances. To this purpose the philosophers say, that Nature does nothing in vain, and more is in vain, when less will serve; for Nature is pleased with simplicity, and affects not the pomp of superfluous causes.   RULE II   Therefore to the same natural effects we must, as far as possible, assign the same causes. As to respiration in a man, and in a beast; the desce...