Hi @vjtorley, @structureoftruth, @jongarvey, @Eddie and others listening,
So I just came back from the 4-day symposium on Thomism and modern science, which focused heavily on the philosophy of chemistry. I’m not yet an expert on A-T philosophy, but I think I’m getting better at it.
Substantial change and the cone of possibility
We talked about this question (and variants of it). The best explanation that I got (inspired by Fr. James Brent, O.P. and Jordan Haddad): you, Vincent Torley, being a physical human being, consists of secondary matter, i.e. prime matter which has substantial form. Thus your potentiality is limited by actuality. This means that while you do have the capacity for substantial change, you only have a limited number of things that you can substantially transform into within your “cone of possibility”. Now, in principle an external cause with infinite power (i.e. God, who is pure actuality) could act upon you and substantially turn you into a raccoon or car. But if what we have are only natural causes with limited actuality, then you are stuck within that cone of possibility. You can only transform into a corpse when you die.
The composition of water
The next topic concerns what water is. Is water composed of H2O? First, I’d like to narrow down and clarify the scope of the problem from water to H2O molecules. In a random body of water, there is H2O, but also other free radicals and other molecules, so this would confusing. Instead, we’re going to ask a simpler question: do hydrogen and oxygen exist actually or virtually in an H2O molecule?
The Thomistic answer is usually the latter, as Thomists tend to be against chemical reductionism. Chemistry is not a strict result of the laws of physics. I found out that this is by no means a minority or fringe position among philosophers of science, even those who are not Thomists. This is because there are several problems with reductionism, as detailed in this SEP article (section 6) and this paper by Robert Bishop, Whence Chemistry?. In short, in general it is currently impossible to completely and exhaustively work out the properties of molecules from their constituent atoms, even if we’re only talking energy levels. A good test case is isomers, molecules which have the same chemical formula but different structure, causing them to have different properties. Currently, there is no way for a quantum chemist to calculate the properties of different isomers without manually inputting the chemical structure. Of course, perhaps someone someday will find a way to do so. But there seem to be serious conceptual obstacles if we only have QM. These issues and others are talked about in more detail in the Bishop paper.
Thus, hydrogen and oxygen only exist virtually in H2O, which is its own thing, with different properties than either hydrogen and oxygen. Now, there are some properties that water may have in common with either atom. But this reflects the reality that to exist virtually means to have the powers of hydrogen and oxygen affect (though not fully determine) the properties of H2O. Therefore, it is unsurprising that these commonalities exist.
Once this argument works, you can go on and argue that a body of water could be thought of as a single substance consisting of H2O molecules all existing virtually within it. Some properties of a body of water, such as surface tension, apparently do not make sense to talk about if you have only a few molecules of water. The existence of macro-level properties irreducible to its constituents points towards its constituents existing only virtually.
Next, Robert Koons was one of the main lecturers in the symposium, and he talked about his own specific views on the philosophy of chemistry. Some of his ideas are summarized in this paper we read: Hylomorphic Escalation: An Aristotelian Interpretation of Quantum Thermodynamics and Chemistry. He takes the view, common among Thomists, that only macro-level objects with thermodynamic properties exist. Elementary particles/fields and even atoms for the most part exist only virtually as part of a greater object. Koons’ paper gives a fairly persuasive argument that thermodynamics cannot be reduced to a collection of discrete, individual particles. But in general, one of the main reasons why Thomists are reluctant to think of elementary particles and fields as individual substances is because in practice, we almost never (if at all) find them existing by themselves (instead of as part of some other substance). Thus, Thomists tend take a more structural realist view (as Feser does) towards the reality of atoms, molecules, and elementary particles.
Now, I would not go as far as Koons and say that electrons, for example, are never a substance on their own - there are specific situations where you can trap individual electrons, for example. But for the most part, the vast majority of electrons we encounter daily are never encountered on their own. They do not have their own unity, but are always part of some atom in a solid or liquid with their own macro-level properties.
Overall, after this symposium I became more aware of the problems with reductionism and the plausibility of Aristotelian philosophy of science to solve some of these problems. Still, I had many unanswered questions, partially because many of them are active research areas for Thomistic philosophers of science. For example, it is not clear whether light is a substance (or perhaps the EM field which gives rise to it is). I realized that in many areas of physics, it is still awkward to interpret them with A-T philosophy. I think that much more work still needs to be done, even if there are many areas where A-T philosophy is clearly useful. It is indeed a puzzle to me why A-T philosophy seems useful to understand science holistically, but when actually doing and thinking about science, it’s just much easier to revert to an atomistic model of nature consisting of building blocks which form together into a bigger whole.
Most scientists would probably not appreciate the uses of A-T philosophy, as it is probably not going to be beneficial for the practice of science itself. (This is unsurprising, as it is the same case with philosophy of science in general.) You certainly can be a scientist and take the “shut up and calculate” or “I have no need of that hypothesis” approach. However, A-T philosophy gives a better philosophical explanation for why science is possible at all, for example with regards to the laws of nature, which prompted this thread in the first place.