Part III, Preface
Most writers on the emotions and on human conduct seem to be treating rather of matters outside nature than of natural phenomena following nature's general laws. I shall consider human actions and desires in exactly the same manner as though I were concerned with lines, planes, and solids.
Part III, Prop. II, Note
No one has hitherto laid down the limits to the powers of the body; that is, no one has as yet been taught by experience what the body can accomplish solely by the laws of nature.