Aristotle: Reason and Nature

5.1 The Life of Aristotle

Aristotle’s 20 years at Plato’s Academy were followed by time spent doing philosophy and conducting research in marine biology. After a stint tutoring the boy who would become Alexander the Great, Aristotle returned to Athens and founded a school called the Lyceum. But political upheaval meant a charge of impiety against him, and he fled. Shortly thereafter, he died at age 62.

5.2 Logic, Knowledge, Truth

In contrast to Plato, Aristotle trusts the senses to yield knowledge of the world. In fact, such knowledge begins with sense experience. By codifying a logical system, Aristotle developed a theory of how such experience yields knowledge.

The heart of his system is the syllogism, which can demonstrate not only what is the case, but also why; it allows us to evaluate whether a proposed explanation of a natural occurrence is correct. When the premises are necessarily true, the proof demonstrates that the conclusion follows. Since not every statement is demonstrable, there will be some premises that he thinks can be known intuitively.

5.3 Physics and Metaphysics


Substance is Aristotle’s answer to the questions, “What is being?” “What is real?” and “What is fundamental?” Linguistically, substance is the subject of a proposition. It’s that which, in a sentence, is identified in answer to the question, “What is it?” Predicates tell us about the subject, so it is in virtue of the subject that the predicates are (or the predicate is).

Everything is parasitic on the subject, but this does not mean that substance remains when properties are removed—mere matter. Yet substance is also not mere form. So, substance cannot be either one of these things alone but may be them combined, at least so far as matter and form constitute the essence of the thing: substance = matter + form-as-essence.


Aristotle, unlike, for example, Parmenides, claims that change is real. Change does involve sameness, at least to a certain extent, since there is something that persists through change. That is the subject of change. There is also a pre-change and post-change situation, in which the subject exists prior to and after modification. Change occurs either in the matter (to produce a new substance) or in the non-essential properties of a substance.


Aristotle’s four causes are formal (its shape), material (what it’s made of), efficient (what triggered the change), and final (end or purpose of change, of what a thing is).


The development or function of a thing is toward a goal or point—the reason for being. Nature does not change or move without purpose or without a telos. Nature is teleological.

5.4 Happiness, Virtue, and the Good

Aristotle’s conception of telos finds its way into his ethics. We can say, for example, that a lawyer practices law, but a good lawyer is one who practices law well. The value is in the activity, which produces excellence in the individual. Excellence in the individual is called virtue when one has a disposition to behave in line with a standard of conduct. That standard serves as a mean between extremes (e.g., courage is a mean between the extremes of cowardice and viciousness). When we become virtuous, we live a good life.

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