Faith clearly teaches that this world did not exist from all eternity, but was created in time, i.e.,a measurable span of time has elapsed since the world came into being. Saint Thomas and Suarez deny that we can prove from reason that eternal creation was impossible, that this world could not have existed from all eternity. Many modern philosophers think we can prove it. The difference is only apparent. The former spoke of a priori arguments, of which there are none; the latter speak of arguments drawn from experience, e.g., the transformation of energy, or radioactivity.