Changing Science: From Aristotle to Modernity

Rejection of Aristotelian Science

A major shift in the way science was pursued occurred in the 17th century. Prior to this time, science was “Aristotelian” in the sense that nature (the physical universe) was viewed as teleological and essentialistic.

To see the natural world as teleological was to see all motion or change as goal-oriented, whether this motion was the growth of a plant, the rolling of a stone down a hill, the burning of a piece of wood, or any other change. Things fell not because of gravitational attraction, but because they were striving toward their proper place. An object pushed across a surface — say, a ball across a table — would slow down not because of friction, but because such motion was not natural to it. To view the world as essential­istic was to view each kind of thing (for instance, dogs, human beings, oak trees, stones) as possessing a certain nature or essence that determined its behavior (including, of course, the kind of motion natural to it).

Aristotle’s essentialism focused on objects that are readily observable, and in this sense his science was highly empirical: if you couldn’t see it, taste it, feel it, then it didn’t exist. This might seem like a good approach for science to take but, as anyone who has explored the natural sciences will know, the world is rarely as it first appears. The building blocks of nature — whether they are atoms, electrons, waves, quarks, or superstrings — generally are not empirically observable. So while Aristotle’s naive empiricism, along with his essentialistic and teleological view of nature, served the natural sciences quite well for a millennium or so, it eventually got muddled down with problems — and this was the state in which Descartes, Galileo, and a few other clear minds found the sciences of their own day in the 17th century.

The New Science

Galileo Galilei (1564-1642) embodied as well as anyone the spirit of the age. His Dialogue Concerning the Two Chief World Systems (1632) defended Copernicus’s heliocentrism by arguing against the dominant Aristotelian geocentric cosmology. For this he was summoned before the Papal Inquisition at Rome, and on June 22, 1633, was forced to recant his belief that the earth moves (after which he is said to have muttered under his breath: “Eppur si muove” — “But it does move”), and was placed for the remainder of his years under house arrest. He is sometimes credited with having invented the telescope, but in fact crude versions were already being manufactured in Holland before Galileo. His achievement, rather, was to improve this instrument (his first telescope — Galileo used the word perpicillum — magnified only about 3x, but within a few months he had managed to create a 20x scope) and to use it to study the heavens, whereupon he discovered that the moon has mountains and craters, that the sun has spots, and that Jupiter has moons (none of which is consistent with Aristotelian cosmology). This was in the fall of 1609, and he quickly published his findings in a short work called the Sidereus Nuncius or Starry Messenger in March 1610, which made him instantly famous. But Galileo’s most important contribution wasn’t his telescopic observation so much as his emphasis on a mathematical understanding of the world, and his claim that initial observations rarely reveal to us the true nature of things.

Two characteristics of modern science as it was being developed in the 17th century set it apart from the way science had been done in the past: it was based on experimentation and it was mathematical. The external world of tables and chairs is now something whose true description consists of mathematical formulas. If it can’t be captured with numbers, then it doesn’t really exist, or at least cannot be the object of science.  “The book of nature,” claimed Galileo, “is written in the language of mathematics.”

René Descartes (1596-1650) expressed this same understanding of science at the end of his Second Meditation, when he claims that our knowledge of bodies comes through the intellect (using mathematics) rather than through the senses:

I know that bodies are not, properly speaking, perceived by the senses or by the faculty of imagination, but only by the intellect, and … I know that they are not perceived by being touched or seen, but only insofar as they are expressly understood.

This amounted to an explicit rejection of Aristotelian teleology and essentialism: the essence of a thing cannot be described mathematically, nor can its purpose or end. What can be reduced to numbers is the size and shape of a thing, and whether it is in motion or at rest. This motion, furthermore, was to be explained in terms of mechanical forces, all of which are quantifiable, and thus amenable to the language of mathematics. Descartes believed that all of Aristotle’s talk of formal qualities (being a dog, being furry, being brown) is reducible to these so-called “primary qualities” of size, shape, and motion/rest. Even the four basic qualities of the Ancients (hot, cold, dry, wet) “can be explained without the need of supposing for that purpose anything in their matter other than the motion, size, shape, and arrangement of its parts” (The World, ch. 5). Descartes was fully aware of the revolution he was pulling off in his Meditations on First Philosophy; in a letter to his friend Marin Mersenne (January 18, 1641) he wrote:

I may tell you, between ourselves, that these six meditations contain all the foundations of my physics. But please do not tell people, for that might make it harder for supporters of Aristotle to approve of them. I hope that readers will gradually get used to my principles, and recognise their truth, before they notice that they destroy Aristotle’s principles.

If only to make the world seem even stranger, the basic stuff of this world no longer consists of dogs, human beings, or oak trees, but rather of atoms (or corpuscles, as they were called by Descartes) — tiny solid objects (invisible to the unaided eye because of their small size), with a definite size and shape. It is the size and shape of these atoms that give them their other properties — for instance, vinegar tastes sour because the “vinegar atoms” have little hooks that prick the tongue. The unobservable features and behavior of the atoms explained the observable characteristics of the larger objects they composed.

The early 20th century saw the rise of a new model of atoms that understood them as con­sisting of a dense nucleus orbited by electrons, somewhat like the planets of our solar system orbit the sun. The implications of this model are rather startling. For instance, the chair we are sitting on and the floor on which we stand, while they appear to be quite solid, are in fact mostly empty space, the distance lying between the nuclei and their electrons being quite immense. The chair and floor do not appear to be 99% emptiness, but that is what they indeed are, according to the new science. (This account of physical objects is already out-dated; a more up-to-date scientific account is even more difficult to associate with our normal, non-mathematical experience of “the world.”)

The new scientists also came to appreciate the importance of experi­men­tation, of testing their hypotheses against the sense-data of experience. The natural world was the object of study, and so it was similarly the final judge as to the truth of scientific claims. If hypotheses are routinely checked against the data of the senses, foolish assertions such as we occasionally find in Aristotle (for example, that men have more teeth than women, or that bees emerge spontaneously from manure) will always be short-lived and quickly disproved. Aristotle was an acute observer of nature, but he often relied on written authority and hearsay, and failed to check this hearsay against nature itself.