The works of Aristotle are of special interest in the history of science, not just because of his physical theories and their immense influence, but also because of his profound interest in how we should organize and understand our knowledge of nature. In Posterior Analytics, Aristotle offers the first technical definition of knowledge, episteme, as an organized body of deductive arguments. Although Aristotle did not himself adhere to his own rigirous requirements for presenting knowledge, the idea of establishing strict conditions for what counts as knowledge and for its presentation was highly influential.
Aristotle's Physics sets out a program for how to study nature. He argued that to know about a thing or a phenomenon one has to consider its four causes: first the material cause, which asks what something is made of; second the formal cause, which concerns its shape or organization; third the efficient cause, which is the agent or "origin of change" that produced the thing; and last the final cause, which is the "end" or purpose of something. For Aristotle nature is directed toward the best. The teleology in Aristotle's approach to nature is particularly evident in his thoroughly researched biological treatises where functional explanations play an important role.
In Aristotle's account of the cosmos, all matter on earth consists of combinations of four elements: earth, water, fire, and air. Each of the elements has a natural direction of motion: downward for the former two, and upward for the latter. Thus the Earth is situated in the center of the universe, while air and fire move outward toward the heavens. The cosmos is divided into two distinct spheres. The terrestrial sphere is characterized by change, force, and the movements of the four elements. The celestial on the other hand is unchanging, and the heavenly bodies are made of a fifth element, ether, which moves in perfect circles, thus accounting for the regular circular motions of stars and planets.
In general Aristotle's work is characterized by a lack of dogmatism and a willingness to adopt new methods to deal with the problem at hand. Later Aristotelianism produced influential systematic accounts of Aristotle's work, but these do not reflect the breadth of Aristotle's interests and approaches.