I think most of us realize that the human mind embraces all of reality, not just scientific or artistic reality. Science and the arts (which includes philosophy and writing) are two ways of approaching the same reality.
The Roman philosopher Lucretius wrote a long poem called De Rerum Natura, or On the Nature of Things. This was back when philosophy was the pursuit of all knowledge, and that is pretty much what Lucretius had in mind in writing this work. The ancient Greek and Roman philosophers have the reputation—a reputation I have often propagated—of imagining the way the universe ought to be, rather than finding out what it is really like. It took the advent of science to reveal reality. But Lucretius did two of the most important things that scientists do: he was observant, and he tested hypotheses about what he saw. He was extremely limited in what he could see, but he did the best he could.
Lucretius could not see atoms. But he believed that everything was made out of them. He called them by such terms as “primal bodies” and “seeds.” He left to Democritus the distinction of inventing the word “atom,” which means “indivisible.” You cannot see them, but there are a lot of things you cannot see: the wind, scents, heat, cold, evaporation, to name a few. He included both matter and energy as primal bodies, just as we talk about atoms, electrons, and photons. He hypothesized that invisible air consists of primal bodies that are always moving and bouncing. He then tests this hypothesis: How do we know this? A shaft of light shows motes of dust moving; there must be matter pushing them around. Thus, starting with the invisible world of atoms, he moves to hypotheses that anyone can test just by looking at the world around them and thinking about it.
Lucretius speculated about what these primal bodies were like. For one thing, they do not have color. How did he test this hypothesis? If primal bodies did have color, they could not change color, as when a dark sea becomes foamy. It is changes in the arrangements of primal bodies that change the colors of things. One may question the way he tested the hypothesis that atoms do not have color, but he tried.
And matter, said Lucretius, is eternal. Matter cannot vanish. If it could, then by now it would all be gone. In this simple observation is a primitive version of a scientific hypothesis. Instead, Lucretius said, the death of one thing becomes the birth of something else. Things grow, and things decompose, as primal bodies enter new combinations and arrangements. In this way, nonliving matter can become living matter. He gave examples. One of them, worms from mud, was wrong; but he also said that, in terms of matter, grass becomes cow, cow becomes human, and humans become food for vultures. The world is built of primal bodies as sentences are from words and words from letters. From a few letters, as from a few kinds of primal bodies, diversity emerges.
Furthermore, Lucretius said that there are no miracles that make matter and organisms pop into or out of existence. How do we know this? We know this because, if such things ever happened, surely we would have noticed them. Why don’t we see humans popping into existence in the sea, or fish on land? Because they come from pre-existing matter. Once again, this is a primitive kind of hypothesis-testing, regarding things that seem perfectly obvious to us but may not have been to ancient thinkers.
Lucretius applied some of his best hypothesis-testing to religious assumptions. Does the body have a soul? Even today people assume this is merely a matter of faith. But Lucretius made it into a testable hypothesis. If the soul could leave the body, then it would, moving from high concentration to low, leaving a cold dead hulk behind. Therefore, when the body dies, so does the soul. The soul grows then degenerates long with the body. His evidence? When the body is sick, the soul suffers also. People rave or faint when their bodies are ill. When the body gets drunk, so does the soul. The soul, not just the body, can be cured by medicines. Just as a nose will rot if cut off from the body, so will the soul; it must be part of the body. If the soul is immortal, why is it, Lucretius asks, that people are frightened while dying? In fact, why does a soul fear death? And how do they get into human bodies? Do souls wait around for the chance to jump into fetuses? And if our minds are souls, why do we forget things? And why do we assume that souls, like bodies, have five senses? Finally, if the soul is a separate and eternal thing, why do we not remember events that occur before our births? “Look back once more and see how all the lapse of everlasting time before our birth was naught to us.” And so will be the time after our deaths, says Lucretius. If souls are separate from bodies, then why don’t souls and bodies once in a while mismatch? Why don’t you have doves with hawk souls or hawks with dove souls, that is, why don’t doves ever chase hawks? Why are there no animals with human intelligence? You’d expect that a human soul would once in a while end up in an animal. Two thousand years ago Lucretius was applying critical thinking to questions that many people still approach with fuzzy thinking.