Chapter OneThe Fundamental Question: How Do We Know?
We should not be too confident in our belief of anything.-Cicero,
Tusculan DisputationsA number of years ago, I took a trip to Yellowstone National Park with my daughter, Caley, who was eight years old at the time. It was just the two of us, enjoying the wilderness and the freedom to drive around the park, looking for bison and rocky outcrops. One day I casually said that we would soon need to get some gas because we were running low. My daughter asked: "How do you know that?" I looked at her and said, "You know, Cal, that is probably the most important question you can ever ask." I proceeded to explain about fuel gauges and what little else I knew about the mechanics of cars. To this day, Caley-now a journalist for the BBC-keeps asking that very same question, "How do you know that?," to lots of people. Some welcome it, many get annoyed. And I still think it's the most important question a person could possibly ask, for the simple reason that everything else depends on answering it in a satisfactory manner.
Philosophy Before SocratesPhilosophy is classically characterized as having a number of branches that run the gamut of what human beings are interested in exploring: metaphysics investigates the nature of the world; logic teaches us how to think; ethics considers how we should live our lives; political philosophy deals with how to build a viable and just society; and aesthetics addresses the tricky question of what is (and is not) beautiful. But arguably the most fundamental of the branches of philosophy is epistemology, which deals with the nature of knowledge. How do we know anything? The answer to that question must logically precede all the others, because for whatever is asserted in the realms of metaphysics, ethics, and so on, someone could (indeed, should!) reasonably ask: How do you know that?
Western philosophy began because some people were dissatisfied with standard answers to the epistemological challenge. The early philosophers, known as the pre-Socratics (in a moment, we'll get to why that strange name), took the crucial step of rejecting mythological answers to questions about how the world works, turning instead toward answers rooted in a naturalistic understanding of things. It wasn't just the beginning of philosophy, it was the beginning of science.
Certainly, the initial steps were hardly convincing from a modern perspective. When Thales of Miletus (626-548 BCE) said that everything is, at bottom, made of water, he was wrong. But he did two fundamental things that changed the way we think about the world: First, he dismissed "explanations" rooted in supernatural and miraculous events, on the grounds that they do not, in fact, explain anything. Second, Thales introduced the notion that there must be a fundamental substance that the world is made of, despite superficial appearances to the contrary. That idea still drives modern physics with its ongoing quest for a "theory of everything."
Two of Thales's students, Anaximander and Anaximenes, also from Miletus (in modern western Turkey), proposed alternative hypotheses about the basic nature of the world. For Anaximenes, the arche-the unified principle underlying everything-was air, another of the classical four elements (together with water, fire, and earth). Anaximander, however, was more sophisticated and thought that the arche was something he called the apeiron, often translated as "infinite" or "limitless." He proposed the very modern idea that the fundamental substance, which we cannot sense directly, gives rise to the sort of stuff we do sense, like the four elements. And those, in turn, make possible everyday objects like mountains, trees, and human beings. Moreover, when something dies or is otherwise destroyed, its constituent parts are recycled into the apeiron. Invoking Anaximander in the context of quantum mechanics, physicist Max Born said that we could think of elementary particles and their quantum states as manifestations of an underlying substance, which he proposed calling apeiron.
The pre-Socratics were very much ahead of their times, because they often ran into problems answering Caley's question: How do you know that? For instance, why did Thales think that water is the arche? We don't have any direct evidence from the man himself, but we have a passage from Aristotle (384-322 BCE) where he speculates about how Thales reached that particular conclusion:
Thales says that it [the nature of things] is water. . . [Thales's] supposition may have arisen from observation . . . that the nurture of all creatures is moist, and that warmth itself is generated from moisture and lives by it; and that from which all things come to be is their first principle. . . . Besides this, another reason for the supposition would be that the semina of all things have a moist nature.
This indicates that the pre-Socratics understood the basic principle of science: Not only must our conclusions be backed by reasoned arguments, but those arguments need to be grounded in empirical evidence. And therein lies the limitation of their approach: In the sixth century BCE, and for a long time after that, humans simply did not have sufficient technical means to gather compelling empirical evidence for their speculations about the nature of reality, which is why their explanations seem so simplistic to us moderns. We benefit from the scientific revolution that began in the seventeenth century-almost two and a half millennia after Thales.
This did not stop the pre-Socratics from making some stunning discoveries. For instance, based on the writings of Aristotle, modern scholars think Thales understood that the earth was spherical, not flat. Moreover, Herodotus tells us that Thales was the first to successfully predict an eclipse of the sun, on May 28, 585 BCE.
The Socratic TurnDespite the achievements of Thales & co., what Aristotle would eventually call "first philosophy" (and we refer to nowadays as metaphysics) did run into severe limitations when it came to satisfactorily answering Caley's question. Which brings me to the Socratic turn and why we refer to all philosophers before Socrates as pre-Socratics. Our guide Cicero tells us what this turn consisted of:
Socrates was the first who brought down philosophy from the heavens, placed it in cities, introduced it into families, and obliged it to examine into life and morals, and good and evil.
According to Cicero, Socrates reoriented philosophy toward human affairs. In so doing, he also introduced a different method of philosophizing, a new approach to the all-important "How do you know?" question, one that's still practiced today under the name of the Socratic method. Socrates himself explains why he decided to do philosophy differently from his pre-Socratic (he didn't use that term) predecessors:
Having once heard a person reading from a book, written, as he said, by Anaxagoras, and which said that it is intelligence that sets in order and is the cause of all things . . . I was delighted to think I had found in Anaxagoras a preceptor who would instruct me in the causes of things. . . From this wonderful hope, however, my friend, I was speedily thrown down, when, as I advanced and read over his works . . . he appeared to me to be very like one who should say that . . . [the] reason I am now sitting here, [is] because my body is composed of bones and sinews and that the bones are hard, and have joints separate from each other . . . and ten thousand other things of the kind, omitting to mention the real causes, that since it appeared better to the Athenians to condemn me, I therefore thought it better to sit here, and more just to remain and submit to the punishment which they have ordered.
Socrates is saying that Anaxagoras and other pre-Socratics were looking at human behavior in the wrong way. They were using what today we would call a reductionist approach, explaining things exclusively with reference to their elementary constituents. What Socrates says Anaxagoras is doing is, in a sense, not wrong. It is the case that Socrates's ability to sit is made possible by the fine structure of his bones, sinews, and all the rest. But that's irrelevant when explaining why Socrates is sitting in prison in Athens, awaiting his death. The reason for that is to be found in the fact that the Athenians condemned him for impiety and corruption of the youth, and that although he thought the verdict was unjust, he decided to submit to it on the basis that we don't get to pick and choose when to obey the law.
We still have not learned the lesson imparted here by Socrates. Too many modern scientists and science popularizers think that what is really going on with human behavior is to be found at the level of the brain (if they are neuroscientists), or the level of DNA (if they are molecular biologists), or the level of quarks (if they are physicists). In fact, all those levels contribute to our understanding of human behavior, but in a lot of cases when we ask "Why is this guy doing that?" we are concerned with his motivations and the sociocultural and historical background in which he happens to exist. We simply don't get that information if we look at brains, molecules, or subatomic particles.
If this is true, then it turns out that "How do you know that?" also requires the pertinent level of analysis to be specified, which depends on the particular question being asked. If we wish to know why Socrates is sitting in an Athenian cell awaiting his hemlock, the most informative levels of analysis are social and ethical, not anatomical.
On PietyI mentioned the Socratic method, but what is it? Perhaps the best way to answer that question is to see it in action. Here is a bit from one of my favorite dialogues featuring Socrates at work, the Euthyphro by Plato. Let me set the scene. Socrates is on his way to the Athenian court, to which he has been summoned to answer the charges that eventually will lead to his trial and execution. Along the way, he meets a pompous priest named Euthyphro, who is absolutely convinced that whatever he does is "pious"-that is, in agreement with the will of the gods. Intrigued, Socrates begins an exploration, with the grudging help of Euthyphro, of the apparently intertwined concepts of piety and what is loved by the gods. After a while, it becomes clear that Euthyphro has no idea what he's talking about.
Socrates. The point which I should first wish to understand is whether the pious or holy is beloved by the gods because it is holy, or holy because it is beloved of the gods.
Euthyphro. I do not understand your meaning, Socrates. . . .
Socrates. What do you say of piety, Euthyphro: is not piety, according to your definition, loved by all the gods?
Euthyphro. Yes.
Socrates. Because it is pious or holy, or for some other reason?
Euthyphro. No, that is the reason.
Socrates. It is loved because it is holy, not holy because it is loved?
Euthyphro. Yes.
Socrates. And that which is dear to the gods is loved by them, and is in a state to be loved by them because it is loved by them?
Euthyphro. Certainly.
Socrates. Then that which is dear to the gods, Euthyphro, is not holy, nor is that which is holy loved by the gods, as you affirm; but they are two different things. . . .
Then we must begin again and ask, What is piety? That is an enquiry which I shall never be weary of pursuing as far as in me lies; and I entreat you not to scorn me, but to apply your mind to the utmost, and tell me the truth.
Euthyphro. Another time, Socrates; for I am in a hurry, and must go now.
By the end of the exchange, Euthyphro beats the hastiest retreat in the history of philosophical dialogues. But the meat of it-and of the Socratic method itself-is that Socrates keeps probing Euthyphro, gradually showing that his interlocutor doesn't know what he thinks he knows. Notice that the dialogue ends in what the Greeks called aporia, loosely meaning "confusion." Socrates doesn't provide the answer to the fundamental question of whether something is beloved by the gods because it is holy, or holy because it is beloved of the gods. Indeed, he professes not to know anything, and it is precisely this awareness of his own ignorance that made him, according to the oracle at Delphi, the wisest man in Greece.
Stoic ImpressionsOne school of thought that disagreed with the Delphic oracle's conception of wisdom as ignorance was Stoicism. With all due respect to Socrates (which they did have, since they referred to themselves as Socratics), the Stoics thought that a wise person, a sage, was characterized precisely by the fact that he knew things-with certainty.
The Stoics and both branches of skepticism (more on that distinction later) engaged in a multigenerational discussion on the nature and possibility of knowledge. This discussion will provide the epistemological background for everything else I will be proposing in this book. It also answers Caley's question in a satisfying way.
Let's begin with a neat summary of the Stoic take, provided by Cicero himself in his Academica, a book that conveniently recapitulates two and a half centuries of discussions:
Zeno professed to illustrate [the Stoic theory of knowledge] by a piece of action; for when he stretched out his fingers, and showed the palm of his hand, "Perception," said he, "is a thing like this." Then, when he had a little closed his fingers, "Assent is like this." Afterwards, when he had completely closed his hand, and held forth his fist, that, he said, was comprehension. From which simile he also gave that state a name which it had not before, and called it katalepsis. But when he brought his left hand against his right, and with it took a firm and tight hold of his fist, knowledge, he said, was of that character; and that was what none but a wise man possessed.
Zeno of Citium was the founder of Stoicism. His hand metaphor is meant to make a number of points. First off, our understanding of things comes in degrees. Specifically, and in order of increased confidence, we have: perception, assent, comprehension (katalepsis), and knowledge. Perception is an innate ability shared by all animals: We see, hear, touch, smell, and taste things, which is necessary for our bare survival. Assent, however, is something that only human beings are capable of. It's a cognitive process that lets us move from a preliminary, immediate assessment of things (like "Why is there pizza in my refrigerator if it's not a healthy food?") to a hopefully correct judgment about those things (along the lines of "I better not eat the pizza, because it's not a healthy food").
Copyright © 2026 by Massimo Pigliucci. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
