Many of Aristotle's contemporaries complained that oblivious, powerless gods are unsatisfactory. Nonetheless, it was a life which Aristotle enthusiastically endorsed as one most enviable and perfect, the unembellished basis of theology. As the whole of nature depends on the inspiration of the eternal unmoved movers, Aristotle was concerned to establish the metaphysical necessity of the perpetual motions of the heavens. It is through the seasonal action of the Sun upon the terrestrial spheres, that the cycles of generation and corruption give rise to all "natural" motion as efficient cause. The intellect, "nous", "or whatever else it be that is thought to rule and lead us by nature, and to have cognizance of what is noble and divine" is the highest activity, according to Aristotle (contemplation or speculative thinking, "theōrētikē"). It is also the most sustainable, pleasant, self-sufficient activity; something which is aimed at for its own sake. (In contrast to politics and warfare, it does not involve doing things we'd rather not do, but rather something we do at our leisure.) This aim is not strictly human, to achieve it means to live in accordance not with mortal thoughts, but something immortal and divine which is within humans. According to Aristotle, contemplation is the only type of happy activity which it would not be ridiculous to imagine the gods having. In Aristotle's psychology and biology, the intellect is the soul, (see also "eudaimonia").