His contention was that the abstract truths of the mind-mathematical truths, moral and normative truths about ideals-are what really matter in life and in philosophy, and that the empirical world around us consists of merely poor copies of these ideals. By contrast, Aristotle did as much or more work in what we would today call science (physics, biology, etc. ) as in what remains a part of philosophy. While Aristotle certainly did important work in ethics and related areas, he concentrated as much or more on examining the material world.
Plato can be read at times as being quite disparaging of science. This is not true of Aristotle. Second, the difference in the approaches and values of these two philosophers resulted in very different political philosophies. Platos political philosophy, which can be found principally in the Republic. For him, the just state is one ruled by ascetic philosophers who have been raised from birth not to value material reward or exclusive human connections, even with their own kin. They are the ideal of wise, objective, fair-minded, ultra-rational beings.
In contrast to Platos utopian political philosophy, Aristotles political philosophy, which can be found principally in the Politics, has a large component of descriptive political science. When he does argue for certain political schemes, they tend to be incremental improvements on existing systems. Like his teacher Plato, Aristotles philosophy aims at the universal. Aristotle, however, finds the universal in particular things, which he calls the essence of things, while Plato finds that the universal exists apart from particular things. Aristotle makes philosophy coextensive with reasoning, which he also would describe as science.
Note, however, that his use of the term science carries a different meaning than that covered by the term scientific method. For Aristotle, all science is practical, poetical or theoretical. By practical science, he means ethics and politics; by poetical science, he means the study of poetry and the other fine arts; by theoretical science, he means physics, mathematics and metaphysics. In general, Plato is the more extravagant thinker, the thinking outside the box type who was equal parts brilliant and bizarre in his ideas. Aristotle is more the cool, logical, dry, systematic thinker whose works tend to read like encyclopedias.