Teleology is the study of the ends or purposes that things serve, and Aristotle’s emphasis on teleology has repercussions throughout his philosophy. Aristotle believed that the best way to understand why things are the way they are is to understand what purpose they were designed to serve. For example, we can dissect an animal to see how its anatomical organs look and what they’re made of, but we only understand each organ when we perceive what it’s supposed to do. Aristotle’s emphasis on teleology implies that there is a reason for everything. Just as Aristotle sees purpose in anatomical and biological systems, he sees human life as organized and directed toward a final end as well. Because we are essentially rational, Aristotle argues that rationality is our final cause and that our highest aim is to fulfill our rationality. This argument has a deep impact both on Aristotle’s ethics and on his politics. The good life, for which all our virtue and wisdom prepares us, consists primarily of rational contemplation, and the purpose of the city-state is to arrange matters in such a way as to maximize the opportunities for its citizens to pursue this good life.
The term substance designates those things that are most fundamental to existence. However, since there is no clear or definite answer as to what those things are, substance is effectively a metaphysical placeholder, a word that refers to a problem rather than a definable thing. Aristotle points out that some things do seem to be more fundamental than others. For example, colors can only exist if there are physical objects that are colored, though it seems conceivable that physical objects could potentially exist in a world devoid of color. If there is a hierarchy to being, such that some things are more fundamental than others, there must be a most fundamental thing on which everything else depends. Aristotle thinks that he can approach this most fundamental thing by examining definition. Properly speaking, a definition should list just those items without which the thing defined could not exist as it is. For instance, the definition of a toe should mention a foot, because without feet, toes could not exist. Since we cannot define toes without making mention of feet, we can infer that feet are more fundamental than toes. A substance, then, is something whose definition does not rely on the existence of other things besides it.
Aristotle’s insistence on the primacy of substance reflects his view that there is no single category of being. We can talk about existence in connection with all sorts of things. Colors exist, ideas exist, places exist, times exist, movements exist, and so on. Part of Aristotle’s insight is that these things do not all exist in the same way. That is, there is not some one thing called “existence” in which colors and places partake in markedly different ways. Rather, there are different categories of existence that apply to different categories of things. Colors and places have two entirely different kinds of existences. However, if different sorts of things exist in different ways, how is it that there seems to be a single cosmos in which color, place, time, and all the rest, seem to exist together? The fact that color and substance have two different kinds of existence does not prevent substances from being colored. For the cosmos to be unified, there must be a base unit of existence on which all other kinds of existence depend. Aristotle’s argument for the primacy of substance, then, is his way of saying that it is substance, and not time or location, that binds the cosmos together.
By rejecting Plato’s Theory of Forms, Aristotle clears the way for his empirical approach, which emphasizes observation first and abstract reasoning second. Aristotle received his philosophical education at Plato’s Academy, so it is natural that he would feel obliged to justify at length why he departs from the doctrines of his teacher. He provides detailed arguments against many of Plato’s doctrines in almost all of his major works, focusing in particular on the Theory of Forms. In Aristotle’s view, this theory is essentially an assertion of the superiority of universals over particulars. Plato argues that particular instances of, say, beauty or justice exist only because they participate in the universal Form of Beauty or Justice. On the contrary, Aristotle argues that universal concepts of beauty and justice derive from the instances of beauty and justice in this world. We only arrive at a conception of beauty by observing particular instances of beauty, and the universal quality of beauty has no existence beyond this conception that we build from particular instances. By saying that the particulars come first and the universals come after, Aristotle places emphasis on the importance of observing the details of this world, which stands as one of the important moments in the development of the scientific method.
Aristotle’s methods in biology reveal a great deal about his general methods in philosophy. He was the son of a doctor, and his work shows a particular aptitude for biology. We might contrast this fact with Plato’s aptitude for mathematics. Throughout Plato’s work, we see a continual reference to the forms of reasoning involved in mathematics as the paradigmatic example of what reasoning ought to be. By contrast, we find Aristotle applying the lessons he draws from his biological studies to philosophical questions far removed from biology. Two pertinent examples are Aristotle’s emphases on teleology and classification. Aristotle finds it useful when studying living organisms always to ask what function an organ or a process serves, and from this practical method he infers in general that all things serve a purpose and that we can best understand the workings of things by asking what ends they serve. Similarly, Aristotle develops an ingenious system of classifying the various kinds of living organisms according to species and genus, among other things, and proceeds to find systems for classifying everything from the forms of poetry to the categories of being. Most important, perhaps, is that Aristotle draws from his biological research a keen eye for detail and an emphasis on observation as the key to knowledge.
Aristotle rarely sets down hard and fast rules in the practical sciences because those fields are naturally inclined to a degree of vagueness. Aristotle is generally credited with being the first thinker to recognize that knowledge is compartmentalized. For example, he recognizes that the practical sciences, such as ethics or politics, are far less precise in their methods and procedures than, say, logic. This is not a failure of ethics and politics to live up to some ideal, but rather just the nature of the beast. Ethics and politics deal with people, and people are quite variable in their behavior. In the Politics, Aristotle seems to waver in determining what kind of constitution is best, but this is not so much ambiguity on his part as a recognition that there is no single best constitution. A thriving democracy relies on an educated and unselfish population, and failing that, another form of government might be preferable. Similarly, in the Nicomachean Ethics, Aristotle does not lay down any hard and fast rules regarding virtue because different behaviors are virtuous in different situations. The vagueness of Aristotle’s recommendations regarding the practical sciences are then a part and parcel of his general view that different forms of study require different approaches.
Aristotle’s theology is based on his perception that there must be something above and beyond the chains of cause and effect for those chains to exist at all. Aristotle perceives change and motion as deep mysteries. Everything is subject to change and motion, but nothing changes or moves without cause. Tracing how things cause one another to change and move is the source of many of Aristotle’s most fundamental insights. He believes that all causes must themselves be caused and all motion must be caused by something that is already in motion. The trouble with this belief is that it leads to an infinite regress: if all causes have antecedent causes, there is no first cause that causes motion and change to exist in the first place. Why is there change and motion rather than stillness? Aristotle answers that there must be a first cause, an unmoved mover, that is the source of all change and motion while being itself unchanging and unmoving. To motivate the heavens to move, this unmoved mover must be perfect, so Aristotle comes to associate it with God.