The last three millennia of Western culture have been witness to a longstanding debate about order in the cosmos and how we might come to know it. The roots of modern science reach into Medieval Christian debates about how constrained God might be in acting. Can and does God change things on a whim? Is God limited by previous decisions or, perhaps some greater power? Two famous Scholastic theologians set the stage for science as we know it today.
Aquinas and Ockham
Thomas Aquinas (1225-1274) argued that the universe must be rational and knowable. Further, he was convinced that revelation (found in scripture, tradition, and prayer) must uncover the same order as observation. Our God-given intellect gave us the power to perceive and understand the natural laws that govern our existence. His perspective was called intellectualism (or rationalism) because it emphasizes God’s intellect – constructing rules – and our intellect – perceiving the rules.
William of Ockham (1288-1347) also believed in our ability to understand, but thought that we did so through observing regularities in God’s behavior, not through understanding the rules God used. He thought humans created rules based on our senses and experience. He thought reasoning from sense data was both necessary (without direct access to ideas through our intellect) and desirable (because God could always do new things). His perspective was called voluntarism because it emphasizes God’s will, which is free to do anything at any time.
In the early seventeenth century, Western European philosophers began to ask if we should go about the processes of theology, philosophy, and natural philosophy (science) in a new way. This started what we call the Enlightenment and set the groundwork for modern reasoning about the world. People have been in the business of scientia (knowing, particularly reasoned knowing about the causes of things) since before the Golden Age of Greece (>500 BCE). New perspectives on how we know would shift this broad sense of knowing the to the more constrained “science” of the modern period. Debate continues to this day about what exactly those constraints are, and that debate goes all the way back to the beginning.
Descartes and Gassendi
Two famous French philosophers attempted to reset the rules of reason. Both of them rejected Aristotle’s theories of cause and substance. Both embraced the Epicurean insights of Lucretius, rejecting Aristotle’s formal substances (real things are most fundamentally matter shaped by an idea – often with an inherent activity and end) and replacing them with particles (real things are most fundamentally tiny packets of mass kicked around by external forces). This view has been called the Mechanical Philosophy because it applied Aristotle’s mechanics (the study of human constructed things that have no inherent purpose, only human attributed purposes) to the whole universe. Clearly for both philosophers, the entire cosmos was reconceived as a tool constructed by God.
[NB: the mechanical philosophy is often described as viewing the universe as a mechanism, but the word mechanism has taken on a whole new meaning in light of this shift. Thus I prefer to emphasize the ontological shift – all particles and external forces, no inherent ends. It also reflects a huge shift in epistemology away from rational deduction toward empirical induction, but that happened later, as we will see below.]
The Mechanical Philosophy lets us think of the world as much less complex than we know it to be. It uses the type of simplifying assumptions that are common to modern science (as when physicists treat an object as though all of its mass was located at one ideal point at its center – “point mass,” “center of gravity”). For good and ill, the two thinkers used different simplifying assumptions.
Rene Descartes (1596-1650) was educated by Jesuits and studied law. He pursued a brief career as a freelance military officer, but invested well and was able to live off the proceeds for the last 27 years of his life. Descartes was an intellectualist, like Aquinas. He famously focused on those things that could be known by reasoning alone, without observation (“I think therefore I am”). He achieved the mechanical simplification by moving all of the hard questions outside the physical universe. The physical universe is made up of things that take up space (res extensa). No thing exists (physically) which does not have volume. He did not believe in vacuum, but though the universe was completely filled with particles. Human and Divine intellect, he moved to the realm of mind along with all the ideas they might hold (res cogitans). Descartes used the word anima for mind or soul. Humans had an anima in the realm of mind. It mysteriously communicated with the body through the pineal gland. Human bodies were like automobiles driven by minds, while plants and animals were simply automata like windmills, driven by external forces. It was the distance between the human soul and the physical creation that allowed science to work. That space created “objective” knowledge, held by incorporeal minds.
Descartes eliminated all final causes from physics, though held that God had purposes for the universe. Forms existed and we can reason from them (e.g., matter, as matter, can neither be created nor destroyed; God, as subsistent necessity, must exist.) The idea of the universe is like a great billiards, with atoms clacking against one another purposelessly comes from Descartes. He added to this “physics” a God who had set the balls in motion (but did not intervene) and human minds with cue sticks.
Pierre Gassendi (1592-1655) was a lifelong academic and priest. Like Ockham, he was a voluntarist and insisted that the point of science was to observe the world (and God), which could not be known a priori. By refusing the intellectualist route, he avoided the need for a second realm of mind, but also had to reject certainty in knowledge. We can only achieve probable knowledge based on observed regularities in the universe. He saw this as a pragmatic middle way between the skepticism of Plato (nothing may be known through the unreliable senses) and the a priori dogmatism of the Rationalists (some things are necessarily true). Unlike Descartes, he was happy to say that natural laws applied to a subset of the universe, those things whose regularity was understood by humans. This space allowed God to continue acting in the universe. This space also allowed for actual space, void, or vacuum, that is extension without substance.
Gassendi completely rejected forms, insisting that each thing must be known on the basis of its individual properties (nominalism and voluntarism). Those properties were primarily those of mass, velocity, color, etc. The modern sense of scientific data is much closer to this than to Descartes’ version. Gassendi thought that plants and animals had souls (animae from anima), but that they were physical entities: quickly moving, thin bodies made up of particles. Human souls had an immortal component (animus) specially created by God and added at inception. Gassendi redefined final causes as God’s purposes occasionally visible in the physical world. These external final causes were in line with Aquinas’ thoughts (but only a narrow interpretation of Aristotle’s through the lens of Alexander of Aphrodisias). Unlike Aquinas, he thought our ability to discern them was quite limited.
[NB: Until recently, I associated the mechanical philosophy as strict atomic physicalism. The only things that exist are particles; no particles, no final causes. Turns out that position was rare, though it was posed by Thomas Hobbes (1588-1679) and Englishman known for his political philosophy. Hobbes’ subject, however, was not metaphysics and so this is never developed and seems at odds with a philosophy centered on human agents.]
Descartes’ vision of science was a complete picture of perfect knowledge about the physical world, achieved by minds in another realm. The subject matter was simplified, but the methodology remained open to a priori reasoning. We can comprehend the physical universe precisely because we are not part of it. Gassendi’s vision, on the other hand, embraced only probable knowledge about a subset of the world: those things with regular, sensible properties. The subject matter remained open, but the methodology was constrained. We can make useful models of parts of the universe. Which works better for you? Is science the study of the physical world or the physical study of the world? Or something else entirely?