Philosopher, pupil of Plato, and tutor to Alexander the Great. His work ranged widely over logic, metaphysics, physics, biology, zoology, natural history, history, politics, rhetoric, moral philosophy, psychology, and poetry.

Although his most important works perished, enough survived, principally through Arab sources, that he became the greatest secular authority of the late Medieval and Renaissance world, so much so that for a time his commanding presence stifled further investigation and free thought. This was especially ironic because his surviving work expressed the value of free study and thought above all, both in the form of logic and especially of empiricism, of careful observation of the world around us, of a primary reliance on the evidence of our own senses and our own mind rather than on an external authority, no matter how masterful and prestigious that authority may be.

Aristotle's moral philosophy suggested that happiness should be our goal (Eudamonism), that virtue was a reliable means to this end, and that virtue usually represented a "golden mean" between opposite extremes. This approach to a happy life did not seem to require religion, especially the quasi-mystical religion of Plato, but it did require philosophical contemplation which in turn depended on financial independence or subsidy and the leisure that such independence or subsidy made possible. Supreme happiness was therefore reserved for the few.

Aristotle also emphasized the importance of friendship for happiness, all the more so since women and children were subordinate in classical Greece and thus less suitable for intellectual intimacy. (Montaigne felt the same way in Renaissance France, that psychic, as opposed to physical, intimacy should be reserved for close male friends.)

Other Aristotelian positions are equally rooted in the circumstances of his time, including his positive valuation of political autocracy and slavery. Although he probably regarded both as natural and inescapable, any opposition to autocracy during his lifetime would have been extremely dangerous and futile.