Aristotelian natural philosophy

Revolutionaries want change. They want to overthrow all systems and replace them with new ones. Thus the French revolutionaries wanted to overthrow the monarchy and replace it with a republic. Therefore, if there was indeed a scientific revolution in the 17th century, there are two questions that we need to ask. The first is, what was it that the scientists of the 17th century want to replace? The second is, what was it that they wanted to replace it with? It’s to the first of these questions that we’ll looking in this video. What did early modern scientists want to replace? The short answer to this question is scholastic philosophy. Scholastic philosophy here means the philosophy of the medieval schools or universities.

Scholastic philosophy here includes a wide array of disciplines from logic and ethics to what was called “natural philosophy,” or what we would call science. Scholastic natural philosophy closely followed the work of the Greek thinker Aristotle. Indeed, in the Middle Ages, Aristotle was sometimes referred to just as “the philosopher,” and medieval thinkers such as Thomas Aquinas developed their own ideas by building on Aristotle’s. So let’s take a closer look at the Aristotelian natural philosophy that dominated the medieval universities. The best way to do this probably is to look at one or two natural phenomena and to ask how a medieval thinker like Thomas Aquinas would analyse them. So first of all, consider the transformation of a caterpillar into a butterfly.

According to Aquinas, we’re dealing here with a case of what he called “substantial change,” a process of change where one substance ceases to be but another one comes into existence. That’s when the caterpillar transforms into a butterfly, the caterpillar ceases to be but the butterfly comes into existence. Once the butterfly has come into existence, it will, of course, change in many other ways. For instance, it will grow, and it may change colour. But these are far less radical changes than the change of the caterpillar into a butterfly. After all, when the caterpillar transforms into a butterfly, the caterpillar ceases to be. But when the butterfly changes colour, it survives this change, and it does not cease to be.

Indeed, the change of colour is what Aquinas called an “accidental change,” a change on the level of its contingent, accidental properties. This distinction between accidental and substantial change may be further spelled out in terms of accidental and substantial forms. According to Thomas Aquinas, indeed, a natural body is a portion of matter that has been configured by what he called a “substantial form.” The substantial form of a body was a principle that made it the kind of body that it was. And the substantial form of a body made it move and behave in characteristic ways. You might say that the substantial form of a body was a bit like its inner engine.

The caterpillar in our example, for instance, is a portion of matter that has been configured by substantial form, which makes it look like a caterpillar, smell like a caterpillar, and move and behave like a caterpillar. This same portion of matter gets reconfigured by a new substantial form, which makes it look like a butterfly, smell like a butterfly, and move and behave like a butterfly. Indeed, it is when the same portion of matter gets reconfigured in this way that the caterpillar ceases to be, but the butterfly comes into existence. Accidental change receives a similar analysis. When the butterflies come into existence, the whole compound of matter and substantial form will become subject to further configurations by what Aquinas called “accidental forms.”

These accidental forms account for the contingent or accidental properties that the butterfly has at any given moment of time. They account, for instance, for its specific size or colour or shape. And when the butterfly changes from being, say, blue to being red, Aquinas would say that it loses one accidental form and gains another. This model of analysis in terms of matter and form dominated the medieval universities for centuries. Yet in the 17th century, people like Rene Descartes and Robert Boyle grew dissatisfied with it. And that raises two questions. First, why did you become dissatisfied with this model, and second, what did they want to put in its place. It’s to these questions that we’ll turn in the next video.