John Sellars is the author of Lessons in Stoicism (published as The Pocket Stoic in the US), The Fourfold Remedy: Epicurus and the Art of Happiness (published as The Pocket Epicurean in the US), and numerous other books on Stoicism and Hellenistic philosophy. He is a reader in Philosophy at Royal Holloway, University of London, a visiting research fellow at King’s College London (where he is associate editor for the Ancient Commentators on Aristotle project), and a member of Common Room at Wolfson College, Oxford.

Sellars’s newest book, Aristotle: Understanding the World’s Greatest Philosopher, explores Aristotle’s central ideas on a range of topics, from morality and living the good life to biology and the political climate of Athens. It is lucid and concise, and suitable for both the neophyte and scholars of Aristotle alike—it details the particulars of Aristotle’s thought but also reexamines his importance as a philosopher and scientist more generally.

Sellars kindly agreed to be interviewed by Riley Moore for Quillette in February. The following transcript has been edited for length.

Riley Moore: It’s difficult to discuss Aristotle without discussing everything, because Aristotle wrote about everything—ethics, logic, biology, politics, literature; anything knowable, he investigated it. You go through this in detail in your newest book, Aristotle: Understanding the World’s Greatest Philosopher. Let’s pretend I have never heard of Aristotle. Who was Aristotle, biographically? Was he a pupil of Plato just as Plato was a pupil of Socrates? Is there a direct lineage there?

John Sellars: Yes, there is. Aristotle was originally from northern Greece. His father was a doctor who died when Aristotle was about 10 years old. Aristotle is then brought up by his uncle who had been a student at Plato’s Academy some years earlier. When Aristotle reaches 17 or 18, he goes to Athens to study at Plato’s Academy and stays there for 20 years. Plato is certainly the key point of reference. Socrates, Plato, and Aristotle make up this kind of triumvirate of significant Greek thinkers, and they’re all engaging with their predecessors. We see Aristotle wrestling with Plato’s ideas and ultimately trying to break away from them in order to develop his own independent views. That’s the beginning of Aristotle’s career.

Then Plato dies, and the Academy passes to Plato’s nephew. Aristotle decides that’s a good point to leave. Maybe Plato’s nephew and Aristotle didn’t get on, we don’t know, but he heads off to Asia Minor—what we would now call Turkey—with some other pupils from the Academy who left around the same time. Then he moves just a short distance to Lesbos, which is the nearest Greek island, and starts to study the natural world. In particular, he studies marine biology. He does that for a few years, and then he is invited back north to his home region by Philip of Macedon, the king, to tutor Philip’s young son, Alexander, who goes on to become Alexander the Great. It may have been that Aristotle’s father, the doctor, had been a physician at the Macedonian court. So, there may have been a family connection there.

Alexander grows up after a few years studying with Aristotle and sets off for his great adventure in the Middle East and all the way to India. Philip of Macedon is murdered around the same time, and Aristotle, having been Philip of Macedon’s guest, decides it’s not a very safe environment. So, he returns to Athens and sets up his own school, the Lyceum, as an alternative, in a sense, to the Academy. The last few years of his life were spent primarily in Athens. So, there’s a big early period in Athens and a big later period. There’s a brief interlude where he’s traveling to Lesbos and Macedonia.

RM: It’s speculated that Plato’s death prompted Aristotle to leave Athens when he didn’t inherit the Academy. Philip of Macedon’s death prompted Aristotle to return to Athens. These monumental deaths have a powerful impact on his life.

JS: Yes, that’s true. Of course, when Aristotle comes to Athens he’s an outsider. He’s not an Athenian citizen. This may have played a role in the story. As a non-Athenian, he wouldn’t have been eligible to own property. If the succession of the Academy involved the transfer of property, it may well have been that Aristotle just wouldn’t have been a plausible successor because he couldn’t have owned anything. He’s kind of an orphan and an outsider with this slightly transient lifestyle. But at the same time, his father may have been at the court of Macedon. Aristotle’s obviously got enough private income to devote his life to intellectual pursuits. He’s moving in quite high circles. But at the same time, he doesn’t really have the social stability and security that one might want.

RM: Can you sketch the ground covered by Aristotle’s work?

JS: It covers nearly everything. It covers everything that we think of as philosophy today. Metaphysics, epistemology, ethics, aesthetics, political philosophy, logic. All the things that we would think of as parts of philosophy, he does all of that. But he’s also engaged in a series of wider intellectual pursuits that have now become disciplines in their own right. There’s a sense in which his work really founds the discipline of biology. No one’s done that kind of work carefully and closely—studying particular types of creatures—before him.

He starts with metaphysics when he’s in Plato’s Academy—the most abstract and complex stuff. And then he moves on to the study of nature. One presumes that his later time with Philip of Macedon and Alexander prompted him to become more interested in political questions. He spends time studying literature, thinking about Greek tragedy, thinking about what makes a good work of art. On the one hand, we might think of Aristotle as a kind of research scientist, but these days we wouldn’t imagine a research scientist to also be interested in questions of literary theory. But Aristotle is actually doing both. In our hyper-specialized world today, that rarely happens.

RM: Could you define “metaphysics” broadly? What does it mean to Aristotle?

JS: “Metaphysics” is a modern word. It’s not one that Aristotle himself would have known. According to legend—and some might dispute the story—Aristotle’s lecture notes were lost for a while after his death. One of his pupils inherited them. The notes were just ignored for a century or two, and then they were rediscovered and edited. A series of works about the natural world were grouped together and given the title Physics. And a series of other works were then grouped together and called Metaphysica, meaning “after the physics.” So, the word doesn’t refer to something beyond the physical world or supernatural or anything like that. It’s just the work that comes after the Physics. Aristotle called the content of those works “first philosophy”—the fundamental questions that deal with the most basic facts about the nature of what exists. So, if we’re asking about the nature of being or existence, we’re asking the most fundamental question because it applies to everything. Then we can ask questions like “What’s a living being?” But that’s also a much narrower question because it doesn’t apply to everything that is, it’s just a subcategory.

RM: Aristotle dove into so many topics that he was regarded in the Middle Ages as the philosopher. In the Divine Comedy, Dante labeled Aristotle “The Master of Those Who Know.” But you argue that this approach to Aristotle is anti-Aristotelian. Why is this so?

JS: Go back to Aristotle’s works and look at what he’s doing. Really he’s trying to understand the world around him and put forward some plausible answers to questions. But he’s quite explicit in his more methodological works that the answers that he’s giving are only ever tentative, and that the best explanations he can offer are on the basis of the evidence that he’s got. In one of his biological works, he says this explicitly—evidence should always trump theory. So, if new evidence comes to light, of course, the theory should be adapted. He’s quite explicit that none of his theories should be treated as dogmatic truths. He’d likely be horrified to find that in subsequent generations his theories were treated that way, rather than as a hypothesis that best fits the evidence and that’s always open to revision.

RM: Would Aristotle, then, be opposed in principle to an authority figure in philosophy?

JS: Yes, absolutely. For him, of course, the authority figure would have been his teacher, Plato. And much of his philosophy is trying to escape parts of Plato’s philosophy and develop his own response. There’s a very famous passage in one of his books that says we owe a commitment to our friends, but we owe a far greater commitment to the truth. We ought to avoid any authority figure who stands in the way of our pursuit of the truth.

RM: Aristotle would like to be approached as he approached Plato.

JS: Yes. That’s a good way of thinking about it.

RM: You claim in your book that Aristotle’s influence is so ubiquitous that it’s “imperceptible.” So what does being a true Aristotelian look like?

JS: I think we could draw a distinction between being a dogmatic Aristotelian who’s committed to the letter of what Aristotle says, and a different type of Aristotelian who is committed to the spirit of how Aristotle works. It’s less about the doctrines and more about the method. I think we can be an Aristotelian in that sense of being committed to his method and approach rather than to his conclusions. Most modern scientists are Aristotelians in that sense because they’re following in the wake of his thought. We’re living in a world that has been formed by Aristotelian ideas, whether we like it or not. The foundations he created for biology, for logic, for literary criticism, all of those things have shaped the modern world in ways that we might not anticipate. For instance, his book, The Poetics, in which he analyzes Greek tragedy, lays down a whole series of rules for what he thinks makes a really good story and what makes a really good plot. Hollywood screenwriters still study this closely in order to write movies.

RM: So, when you agree with Aristotle, you’re an Aristotelian. But when you disagree with him, you can still be an Aristotelian. It just depends on your approach to disagreeing with him. Is this correct?

JS: I think so, yes.

RM: Does this suggest that, across all of Aristotle’s disciplines, there is an underlying idea or principle? Is his approach to biology similar to his approach when defining what is distinctly human?

JS: There are some guiding ideas that join it all together, and ideas that he first formulated when he’s studying biology and which he then applies in other domains. Let’s imagine that you’re on a beach with Aristotle, and you’re dissecting a fish and trying to work out how the fish works and what all the different organs do. He would say that if you’re studying an organism like that, you can look at all the different bits of mushy matter and describe them and see what they’re made of and how large they are. But you’re not really going to understand what is going on inside this organism unless you know what each thing is for. The eye is for seeing, for instance. All the different bits of the organism serve a function. That’s the insight he then reapplies in other domains.

Thinking about human beings, he’s going to ask: what’s the purpose of a human being? What are people for? Does that question make sense when thinking about a human being as a whole, as opposed to, say, just an eye or a heart or some other component? And political communities and the different classes of people within them and the different functions that they play in order to make the society work—what are they for? What are their roles and functions? That teleology is the core idea. In Poetics, he says: imagine you’re watching a play or a film and some character comes into the story at a certain point and then disappears. Now, you’re going to expect that character to come back at some point in the future and serve some useful purpose, because otherwise, why were they there at the beginning? But the question you would ask is: what were they for? It’s like Chekhov’s Gun. If a gun is introduced into a play, you’re expecting it to be fired at some point. Otherwise, what’s it doing there?

RM: Aristotle’s central question is: what makes a human being a human being? How does he go about answering this?

JS: He would look for the differentiating characteristics. What separates these animals from other animals? The first is rationality. Humans are also social animals. There are lots of other social animals, of course, but humans are definitely one of the social animals. So, we’re the rational social animals.

RM: So, Aristotle believes that human beings are social animals, but it’s our capacity to reason that really defines what a human being is. But Aristotle also writes a lot about the “soul.” What does he mean by this?

JS: Plato believed that the soul is something distinct from the body; that it transcends the death of the body and can be reincarnated. What we would now think of as the Christian idea of the soul was already in the air. Aristotle rejects that way of thinking about the soul. For Aristotle, the soul is simply that by virtue of which something is alive. So, it’s not something unique to human beings. Let’s say you’ve got a human being and a corpse. As physical objects, they’re more or less identical. But one of them has got something the other one hasn’t. That’s the starting point. He’s talking about a property or feature of a certain type of object—a living object—rather than something that is potentially separable from a body and that could survive independently in the way Plato thought.

That leads us to the broader question: what does it mean for something to be alive? Ultimately, the difference between a living person and a corpse is that the living person can do things and the corpse can’t. They can move, they can perceive, they can think, they can reproduce. And so, this leads Aristotle to define the soul as basically a series of capacities, a series of things that something can do.

RM: Different schools of philosophy have used the word “soul” in a very similar manner to Aristotle—without any religious connotation. I’m thinking of the Stoics, in particular. You write in Lessons on Stoicism that Epictetus conceptualized the philosopher as a “doctor.” What does he mean by this?

JS: What he and the Stoics have in mind is the idea that our souls—our minds—can get sick or disturbed in a variety of ways and could benefit from treatment in the same way as our bodies get physically sick and can benefit from treatment. This idea goes back to Socrates, and it’s really the idea of mental health. Socrates famously describes what he’s doing as “care of the soul.” He criticizes his contemporaries in Athens and says, Look, you all spend a lot of time looking after your bodies and your property and your reputation, but not one of you takes care of your soul. The Stoics take up that idea. They’re particularly interested in the way emotions are produced by beliefs which can have a negative impact on us.

RM: What does it mean to be a Stoic? The modern and popular use of the word generally refers to someone who is composed, or resistant to showing emotion. How well does that map onto Stoicism proper?

JS: The idea that the Stoic is the person with the stiff upper lip or the person who represses or denies their emotions is quite different from the ancient Stoic view. Often, people think that Stoicism is about repressing or denying emotions, and then they attack Stoicism because they say that doesn’t sound like a very healthy thing to do. And, of course, the Stoics wouldn’t have thought this a healthy thing to do either. The Stoics suggest that we try to look at the world in a different way and make different value judgments about things so that we actually don’t experience those negative emotions in the first place. As Richard Sorabji wrote once [in Emotion and Peace of Mind], it’s not about gritting your teeth, it’s about seeing things in a different way so that you don’t have to grit your teeth.

RM: Stoicism strikes me as a practical philosophy, something that can be implemented directly into life. It doesn’t really bother with questions like “Do chairs or tables exist?” It focuses on character and mental health. The three great Roman Stoics—Seneca, Epictetus, and Marcus Aurelius—led radically different lives. Epictetus was a slave, and Marcus Aurelius was the Emperor of Rome. Does this suggest that Stoicism is inherently democratic and universal? That it is applicable to anyone?

JS: I think so. We see a wide range of people drawn to Stoic ideas today. You’ll see people in the military, people in caring professions, people in elite sports, people interested in ecology and sustainability, and people of all age groups and religious backgrounds. It’s not obvious that there’s any particular group that Stoicism appeals to more than any other. Stoicism is, first and foremost, about attending to your beliefs and judgments and developing the character traits that enable you to live your life. And if you’ve got those in place, then you’re going to be able to cope effectively in any environment. That internal work is the most important thing. We’re all familiar with the stories of Hollywood celebrities who become very rich and famous very young. And on the face of it, they’ve got everything, and yet they spiral out of control because they haven’t got the character traits to cope with it. The external environment, no matter how good it is, isn’t enough to enable us to live a good life. But the right character traits will enable you to survive difficult situations and environments.

RM: Do the Stoics believe, like Aristotle, that human beings are social animals?

JS: Yes, absolutely. There are some important differences between the Stoics and Aristotle’s ethical systems, but this is definitely one of the points where they strongly agree.

RM: Aristotle says that the defining characteristic of a human being is our capacity to reason. It seems reasonable to assume, then, that the route to happiness is directly connected to living the life of the mind. The Stoics seem to agree that happiness comes from within. But both Aristotle and the Stoics also believe that human beings are social animals. Doesn’t the life of the mind largely exclude our life as social animals?

JS: For Aristotle, I think there is something of a tension there. And right at the end of his book, The Nicomachean Ethics, he tries to grapple with these different ideas. In the later tradition, this is called living the active life, as opposed to the contemplative life, which Aristotle himself, I think, is quite drawn to. You get the sense that he would very much like to live the life of the mind and not be overwhelmed by the responsibilities that he might have as a social being. But I don’t think the Stoics think we ought to live the life of the mind in quite the same way. The Stoics are much more active and engaged. When they encourage us to pay attention to character, they’re doing that so we can be more effective agents in the world. So, you might take some time off and reflect and so on, but that should only be for a brief period because the goal is then to go out and play your part as a citizen within the wider community. Aristotle, I think, would be quite happy to disappear into a monastery to be left alone with his intellectual pursuits.

RM: But Aristotle didn’t live a secluded life in the ancient equivalent of a study or office. I don’t picture him knee-deep in lagoon water, snatching bugs and fish, or cutting open crayfish and octopi and journaling about their guts. But this is exactly what he did. Should we find a way to talk about Aristotle that doesn’t reduce him to a merely academic figure?

JS: Yes, absolutely. I mean, he’s the research scientist who’s out in the field, not stuck in the study. We do have some anecdotes that suggest he was a fairly bookish figure when he was younger. And many of his works start with a history of the subject. So, he’s obviously doing that kind of research, too. But his object of study is the world around him, whether that be studying the stars and dissecting animals or looking at political communities or going to the theater and trying to understand how plays work. It all involves opening his eyes and looking at the world. He wants to know what everyone else has thought about the world, and that’s where the bookish study comes in. Books help him understand the very real world around him.

RM: I see. So, it’s not necessarily the books themselves that draw him, but the impulse to understand the world. And since books help him understand the world, he becomes bookish.