So when the universe was quickened with soul, God was well pleased; and he bethought him to make it yet more like its type. And whereas the type is eternal and nought that is created can be eternal, he devised for it a moving image of abiding eternity, which we call time. And he made days and months and years, which are portions of time; and past and future are forms of time, though we wrongly attribute them also to eternity. For of eternal Being we ought not to say ‘it was’, ‘it shall be’, but ‘it is’ alone: and in like manner we are wrong in saying ‘it is’ of sensible things which become and perish; for these are ever fleeting and changing, having their existence in time.
Plato, Timaeus (ca. 360 BC) 37C-38B, as quoted by R. D. Archer-Hind, The Timaeus of Plato (1888)