He spent his life writing about everything that he thought about or observed: poetry, ethics, politics, physics, mathematics, anatomy, physiology, and logic, just to name a few of his areas of interest and thought. Officially he is said to have written 150 philosophical treatises. The 30 that have survived show his broad range of subjects of interest. Many of these treatises are considered to probably be lecture notes that he or a student of his wrote. What Aristotle did was to write down his thoughts on subjects as he explored them and thought it through from development to an end. As a result of this, there isn't really a clear, consistent thought system to Aristotle's writings. Instead his writings show the process involved as he thought about things. .
Aristotle wanted to study and to know everything there was to know about his subjects. He was the first person to think out and develop what he saw as the problem with evidence when trying to support a subject. When he first began to think about a problem, he would approach it in a systematic and deliberate way. First he would find out what had been written or said about the subject, then find out what most people thought about or agreed to be true about it, and finally he did a systematic study of whatever he thought was part of or related to the subject. For example, when he wrote about animals he studied over 500 species to make sure that he was knowledgeable enough to back up his thoughts about animals. This method of study is called inductive reasoning: observing as many examples as possible and then, based on these observations, working out a basic principle they have in common. .
Inductive reasoning is the basis of the western scientific method. Plato saw reality in ideas that could only be known by thinking and reasoning about them. Aristotle saw reality in physical objects that could best be known by experiencing them. He saw objects and organisms in terms of what the currently were and of what they could become.
