The first Greek philosopher, or any other Western philosopher, known to us by name was Thales of Miletus, who reportedly lived between the late seventh and mid-sixth century BCE. He is called the first philosopher for two reasons. One is that Aristotle and later writers called him that. The other is that nobody since Aristotle has found evidence of any earlier philosopher. To this day, Thales remains the first person we know about who who practiced the intellectual discipline that came to be known in the West as philosophy. There is no good reason, though, to think that nobody had tried it before him. There is decent evidence that a few intellectuals in India were doing it many centuries before Thales lived. Indian philosophy, though, and Eastern philosophy in general, has had little overall effect on Western thinking, and it is Western thinking that I wish to discuss in these essays.
Nothing about Thales is known for a fact. The earliest surviving references to him are by Aristotle, who lived about 300 years later and whose sources of information about Thales we do not know. There are no references, by Aristotle or any later source, to any writings by Thales, and so the stories we have about the first philosopher are likely to be mostly if not entirely legend. Even as legend, though, they demonstrate that certain ideas had been proposed by somebody and were being discussed in that part of the world at around that time. Whether or not a certain Miletian named Thales was their actual originator, it is rhetorically convenient to assume for the sake of discussion that he was.
Thales apparently was looking for some kind of unity in nature, a single principle from which to begin a logical analysis of the natural world, and he found that principle in water. He thought there was something elemental about water, and so he thought everything originated as water or else in some way actually was water but in a different form. We do not know just why he thought so, because the surviving stories about him do not record his reasoning. But he seems to have set the precedent of attempting, by the exercise of reason rather than reliance on tradition or authority, to identify an elemental substance and the means by which that substance was so diversely manifest in the world as we observe it.
This was to some extent a departure from common sense. The world looks like it is made of different stuffs, not just different kinds of one stuff. Thales seems to have intuited that what we see is not necessarily what we get, that our senses might not be perfectly reliable. But he followed that intuition only so far. Thales also believed the earth was flat. So did practically everyone else in his day, and he apparently saw no reason to question that consensus. To us living more than 2,500 years later, a round earth seems obvious, but it would not have seemed so in a prescientific culture.
Common sense is the reasoning ability that average people are presumed to be born with and that requires no formal education to develop. Common sense, we suppose, would suffice to inform an illiterate peasant farmer that in the event of a drought, he should take whatever measures are available to him to find an alternative to rain for watering his crops. As a source of useful knowledge, common sense has a deservedly good reputation. Much sport has been made of efforts by intellectuals to prove things that are obviously true to Everyman. For example, why should scientists get worked up over Newton's discovery of gravity, when anyone can see that heavy objects always fall to the ground unless something holds them up? As a source of knowledge, though, common sense is a kind of first impression. It is a good guide, but not a perfect one.
A contemporary of Thales called Anaximander took a more careful look at the evidence about the earth’s shape — perhaps observing some things that Thales had overlooked — and he did some thinking about those observations, and by doing that he figured out that the earth could not be flat. The ancient records do not tell us exactly what he observed or how he reasoned about it. It is speculated that he deduced his conclusion from travelers’ reports — or, if he was himself well traveled, from his own observations — of how the stars appeared to shift position as one traveled north or south.
As you move south, the stars seem to shift toward the northern horizon. A star close to the northern horizon will disappear entirely if you move far enough south, and meanwhile stars will appear above the southern horizon that were not there before. The reverse happens if you move north. Anaximander would also have noticed, though, that nothing similar happens when you travel east or west. The stars do move across the sky from east to west, but that motion is constant insofar as it's always the same stars moving east to west. Everybody sees it the same way no matter where they are on the earth and matter how they move around. Anaximander inferred, therefore, that the earth must be curved in the north-south direction but flat in the east-west direction. He said it was shaped like a cylinder, in other words.
Like Thales, he thought the earth rested on an indefinitely large sea and that it had somehow originated from that sea. He also believed that humans and other living things had originated in that sea as well, that terrestrial life had begun as marine life and later moved onto the land. Anaximander, then, is credited with the first proposal that life has undergone a kind of evolution.
Also like Thales, Anaximander is essentially unknown to us except through legends that first show up in Aristotle’s writings. He is credited with giving the first expression to a notion now called the principle of sufficient reason. According to this principle, commonly attributed to Gottfried Leibniz but effectively endorsed by Aristotle, nothing happens without a reason, and it must be a good enough (i.e., sufficient) reason. To say that A is a sufficient reason for B is to say that if A occurs, then B must also occur. This notion is implicit in Anaximander’s thinking about the earth’s place in the universe. Again, we can be sure he was not the first person to espouse the notion, but he is the first person to express it whose name we know or think we know.
Most Greek intellectuals—along with probably almost everyone else in the ancient world—supposed that the earth was at the center of the universe, and Anaximander was no exception there. But he was exceptional in wondering what kept the earth at the center. According to Aristotle, he reasoned that it stayed there because there was no reason for it to do anything else. More specifically, if it moved, it would have to move in one particular direction rather than some other direction; but, from the center of the universe, no direction would be in any way more favorable than another, and so there would be no reason for the earth to move along one rather than some other universal radius. And so, since it could not move in all directions, it moved in none. It has since been determined that the earth does move and the universe has no center, but Anaximander did the kind of thinking that would in due time yield just that determination. He seems to have rejected the assumption that there was something special about the earth that kept it from moving. Instead, according to his thinking, the earth was doing only what any other object would have done under the same condition of being at the center of the universe.
About a century after Thales and Anaximander, Xenophanes tweaked their ideas a little bit, not supposing that he had to believe anything that either of his predecessors had said. (The Greeks apparently prided themselves on being freethinkers.) Instead of one elementary substance, he proposed two: earth and water. Every liquid was a kind of water and every solid was a kind of earth. It is not clear what he had to say about things that were not obviously either liquid nor solid, but it was a step in the right direction toward explaining why different things had different properties while also accounting for their similarities. Xenophanes observed that living things were a combination of earth and water, and so he seems to have speculated that life originated as a primordial mingling of the two elements.
Fossils were already common knowledge to educated people of the sixth century BCE. Xenophanes noticed that many of them, although obviously the remains of things once alive, looked like nothing that was alive now, and he suggested that they were from creatures that had become extinct. This was certainly not Darwinism yet. It was not even quite science as we know it. It was too speculative to be real science. But it was inference from observations, and it relied on no authority or supernaturalistic suppositions.
The first person known to suggest that the earth was a sphere lived at about the same time Xenophanes did. He was Pythagoras, better known for a mathematical theorem that he did not discover but that somehow got named for him. We know nothing directly about Pythagoras because, like his contemporaries, he left no writings that anyone knows about today. Neither do we have anything written by anyone who claimed to have known him. All we have are stories that were being told about him a few generations after his purported lifetime.
Those stories do not say where Pythagoras got the idea for a spherical earth. That he happened to be right doesn’t mean he had a good reason to believe it. He seems to have believed a great of nonsense for quite illogical reasons, and he might well have decided on grounds of some superstition that the earth had to be a sphere. They were his own grounds, though. If the stories have any basis in fact, then he was apparently quite an independent thinker and willing to put up with some persecution on account of it. While those are admirable traits, Pythagoras is good proof that there is a difference between being admirable and being right.
Pythagoras believed not only in a spherical earth but in a moving one as well, that the world orbited a central fire. That fire apparently was not the sun, though, which Pythagoras thought was only a reflection of the ultimate source of light and heat.
The Greeks never developed a concept of scientific rigor as we understand it. Pythagoras was prone to mysticism, reportedly saying things like “everything is number,” and philosophers who came after him in the fifth century also looked among intangible notions for an essence of everything. For Heraclitus (ca. 500 BCE) it was change. He was the one who is supposed to have said that nobody can step into the same river twice. A few years later, Parmenides said there had to be something that was unchanging, and that whatever it was, it must be the fundamental reality of everything. There was no authority telling the ancient philosophers they had to believe one thing rather than another, and most of them fully exercised their intellectual independence. Except among the Pythagoreans, who seem to have attributed some degree of inerrancy to their founder’s teachings, the early Greek thinkers showed no interest in defending any orthodoxy. Each philosopher intended to find his own answers to the questions that interested him, never minding whom he had to disagree with along the way. Of course there have probably always been freethinkers of this sort in every culture, but they often have had to keep their thoughts to themselves. What is notable about ancient Greece is that such disregard for authority was not just tolerated but apparently, with famous but rare exceptions, admired. Greece might not have produced the first culture to promote freethought, but it was the first to leave any records boasting about it.
Thales said water was the fundamental element of which everything was made. Xenophanes said it was water and earth. Heraclitus said they were both wrong, that the basic stuff of everything was fire. Sometime in the mid-fifth century, Empedocles decided that one or two elements were not enough, and he proposed four: earth, water, air, and fire. He was mistaken about the elementary nature of these particular substances, but his taxonomy fairly approximates the four states of matter that are recognized by modern science: solid, liquid, gas, and plasma. (Ordinary fire is not really a plasma, but it is the nearest thing to it that the ancients could have known about.)
Empedocles also proposed a model of organic evolution more sophisticated than those of his predecessors. He suggested that plants and animals arose naturally at some indefinite time in the past from interactions among the elements, and that they had diversified as a result of differential survival of variations—a foreshadowing of descent with modification through natural selection.
At almost the same time, Democritus (or his mentor, Leucippus) proposed the earliest known hypothesis that everything is made of extremely small particles called atoms. This notion could have been combined with Empedocles’s idea of four elements, since each element could have been composed of its own kind of atoms. They were instead viewed as competing hypotheses, however, and for various complicated reasons Empedocles’s thinking won out when Aristotle endorsed it over Democritus’s. Even so, it survived as a minority viewpoint well into the Common Era. There was, at that time, apparently no stigma attached to claiming that Aristotle was wrong about something.
Some readers might have noticed that the ideas we've been discussing all seem more scientific than philosophical. That distinction is a modern idea, not taking firm hold among intellectuals until the 19th century. Until then, the study of nature was just one among several subjects collectively referred to by the ancients as philosophy, and it seems to have been the first. The others, including epistemology and ethics, began to get some attention during or just before Socrates's lifetime. But we must note again: This is what we discern from the surviving documentation, which we perfectly well know is an incomplete record. I'll have some further comments on historical research in the next essay.