Aristotle is a towering figure in the history of philosophy and science. Aristotle made substantive contributions to just about every philosophical and scientific issue known in the ancient Greek world. Aristotle was the first to develop a formal system of logic. As the son of a physician he pursued a life-long interest in biology. His physics was the standard view through Europe’s Middle Ages. He was a student of Plato, but he rejected Plato’s other-worldly theory of forms in favor of the view that things are a composite of substance and form. Contemporary discussions of the good life still routinely take Aristotle’s ethics as their starting point. Here I will offer the briefest sketch of Aristotle’s logic and metaphysics. We will return to his ethics later in the course.


Aristotle’s system of logic was not only the first developed in the West, it was considered complete and authoritative for well over 2000 years. The core of Aristotle’s logic is the systematic treatment of categorical syllogisms:

1.       All monkeys are primates.

2.       All primates are mammals.

3.       So, all monkeys are mammals.

This argument is a categorical syllogism. That’s a rather antiquated way of saying it’s a two premise argument that uses simple categorical claims. Simple categorical claims come in one of the following four forms:

·         All A are B

·         All A are not B

·         Some A are B

·         Some A are not B


There are a limited number of two premise argument forms that can be generated from combinations of claims having one of these four forms. Aristotle systematically identified all of them, offered proofs of the valid one’s, and demonstrations of the invalidity of the others.

Beyond this, Aristotle proves a number of interesting things about his system of syllogistic logic and he offers an analysis of syllogisms involving claims about what is necessarily the case as well.

No less an authority than Immanuel Kant, one of the most brilliant philosophers of the 18th century, pronounced Aristotle’s logic complete and final. It is only within the past century or so that logic has developed substantially beyond Aristotle’s. While Aristotle’s achievement in logic was genuinely remarkable, this only underscores the dramatic progress of the 20th century. The system of symbolic logic we now teach in standard introductions to logic (PHIL 120 here at BC) is vastly more powerful than Aristotle’s and while this system was brand new just a century ago, it is now truly an introduction, a first step towards appreciating a great many further developments in logic. Reasonably bright college students now have the opportunity to master deductive reasoning at a level of sophistication unknown to the world a mere 150 years ago. The methods and insights of modern symbolic logic are already so thoroughly integrated into contemporary philosophy that much of contemporary philosophy would not be possible without it.


While Aristotle was a student of Plato’s, his metaphysics is decidedly anti-Platonist. The material of the world takes various forms. Here it constitutes a tree and there a rock. The things constituted of matter have various properties. The tree is a certain shape and height, the rock has a certain mass. Plato accounts for the various forms matter takes and the ways things are in terms of their participating in abstract and ideal forms to one degree or another. Plato’s metaphysics centrally features an abstract realm of eternal unchanging and ideal forms. Plato’s forms are not themselves part of the physical spatio-temporal world. Aristotle rejects the theory of abstract forms and takes everything that exists to be part of the physical spatio-temporal world. It might thus be tempting to think of Aristotle as a materialist, one who thinks all that exists is matter, just atoms swirling in the void. Some pre-Socratic philosophers could accurately be described as materialists. But this would miss key elements of Aristotle’s metaphysics. While Aristotle denies the existence of an abstract realm of eternal and unchanging ideal entities, his account of the nature of things includes more than just matter. Aristotle holds the view that form is an integral part of things in the physical world. A thing like a rock or a tree is a composite of both matter and form. In addition to matter, the way matter is gets included in Aristotle’s metaphysics.

Among the ways things are, some seem to be more central to their being what they are than others. For instance, a tree can be pruned into a different shape without the tree being destroyed. The tree can survive the loss of its shape. But if it ceased to be a plant, if it got chipped and mulched, for instance, it would also cease to be a tree. That is to say, being a plant is essential to the tree, but having a certain shape isn’t. An essential property is just a property a thing could not survive losing. By contrast, a property something could survive losing is had accidentally. Aristotle introduces the distinction between essential and accidental characteristics of things. This was an important innovation. When we set out to give an account of what a thing is, we are after an account of its essence. To say what a thing is essentially is to list those ways of being it could not survive the loss of. My hair length is not essential to me, and neither is my weight, my having four limbs, or a given body/mass index. But my having a mind, perhaps, is essential to being me.

How a thing functions is a critical aspect of its nature in Aristotle’s view. As an organism, I metabolize. As an organism with a mind, I think. These are both ways of functioning. For Aristotle, what makes something what it is, its essence, is generally to be understood in terms of how it functions. Aristotle’s account of the essential nature of the human being, for instance, is that humans are rational animals. That is, we are the animals that function in rational ways.

Functioning is, in a sense, purposeful. Aristotle would say that functioning is ends oriented. The Greek term for an end or a goal is telos. So Aristotle has a teleological view of the world. That is, he understands things as functioning towards ends or goals, and we can understand the essence of things in terms of these goal-oriented ways of functioning. We still understand people’s actions as teleological or goal oriented. We explain why people do things in terms of their purposes and methods. Aristotle similarly understands natural processes generally as ends oriented. Even Aristotle’s physics is fundamentally teleological. So water runs downhill because it is part of its essential nature to seek out the lower place.

Explanation: The Four Causes

What does it mean to explain something? If we’d like to have some idea what we are up to when we explain things, giving some account of explanation should seem like an important methodological and epistemological issue. In fact, the nature of explanation continues to be a central issue in the philosophy of science. Aristotle was the first to address explanation in a systematic way and his treatment of explanation structures and guides his philosophical and scientific inquiry generally. According to Aristotle, to explain something involves addressing four causes. Here we need to think of “causes” as aspects of explanation or “things because of which . . . .” Only one of Aristotle’s four causes resembles what we would now think of as the cause of something. Three of the four causes, or explanatory principles, are reflected in Aristotle’s metaphysics and will be familiar from the discussion above. Part of explaining something involves identifying the material of which it is made. This is the material cause.

Thales account of the nature of the world addressed its material cause. A further part of explaining something is to give an account of its form, its shape and structure. The chair I am sitting on is not just something made of wood, it is something made of wood that has a certain form. A complete explanation of what this chair is would include a description of its form. This is the formal cause. Pythagoras and Plato introduce the explanation of formal causes. The idea of a final cause refers to the function, end, or telos of a thing. What makes the chair I’m sitting on a chair is that it performs a certain function that serves the end or telos of providing a comfortable place to sit. Again, Aristotle sees final causes as pervasive in the natural world. So part of explaining what a tomato plant is, for instance, will involve giving an account of how it functions and the goals towards which that functioning is aimed. Bear in mind Aristotle’s interest in biology here. A complete biological account of an organism includes both its anatomy (its material and formal causes) and physiology (which involves functioning and final causes). The remaining cause (explanatory principle) is the one we can identify as a kind of cause in our normal sense of the word. The efficient cause of a thing is that which brings it into existence or gives form to its material. So, for instance, the activity of a carpenter is the efficient cause of my chair.

Before Reading

The following selections from Aristotle’s Physics details his theory of causation, which is actually also his METAphysic, and the is a text called Metaphysics ascribed to Aristotle that follows Physics. The is because his students, who put together his lectures into text form, named them as such. The reason is that the prefix “meta” can mean “about” and “before”, so metaphysics are the conditions, the necessities, the realities that exist IN ORDER for the physical world to exist, which Aristotle describes in both texts. This is a little confusing, but do not worry; all that one must remember is the difference and connection between physics and metaphysics and that the proceeding reading gets at both of these!