What is a Theory?

The scientist must set in order. Science is built up with facts, as a house is with stones. But a collection of facts is no more a science than a heap of stones is a house. – J. Henri Poincare.

As my institution is undergoing a massive core curriculum revision, and I’m serving on the curriculum committee, I’ve been thinking a lot about what students should get out of a core scientific inquiry course. If you asked a random person what should be in that course, probably the “scientific method” will be suggested as something all students should know. Depending on whom you ask, what this “method” entails may differ. Another suggestion might be that students should learn the main scientific theories of our modern era. Although a post-modernist might suggest that such theories represent a consensus view of a particular community and may not have the absolute grounding assumed by the common person. (I've been thinking about scientific theory as mentioned in my most recent post.)

This is where Roald Hoffmann (Nobel-prize winning chemist and someone who has dabbled in the humanities) starts in his essay “Why Buy That Theory?” in the magazine American Scientist. Most examples in the philosophy of science, written by philosophers, make use of examples mainly in physics (and occasionally biology). Very few discuss chemistry, so I find it refreshing to read the views of chemists who have thought carefully about the philosophy of their own discipline. My Ph.D. (doctor of philosophy degree) is in chemistry – I should therefore think a little more carefully about the philosophy of chemistry.

Hoffmann writes: “The theory of theories goes like this: A theory will be accepted by a scientific community if it explains better (or more of) what is known, fits at its fringes with what is known in other parts of our universe, and makes verifiable, preferably risky, predictions. Sometimes it goes like that… But much that goes into the acceptance of theories has little to do with rationalization and prediction. Instead, I will claim, what matters is a heady mix of factors in which psychological attitudes figure prominently.”

He argues that simplicity carries a strong aesthetic appeal. Theories that are “beautifully simple and simply beautiful” capture our imagination – they just feel right, and we humans are apt to quick acceptance when we encounter such simplicity. Furthermore, theories that can be communicated well via a story-telling narrative tend to stick and capture our imagination. Theories also need to be “portable” – the wider its applicability across a range of phenomena, the better. Finally, Hoffmann writes that the “best theories are productive, in that they stimulate experiment”. He tells us his theory about theory in an easy-to-grasp story-telling narrative.

I am in the midst of reading the much denser Chemical Discovery and the Logicians’ Program by Jerome Berson, an emeritus professor of organic chemistry who has turned into a philosopher of chemistry. The quote from Poincare at the beginning of this blog post is the opening quote in the book’s second chapter: “Theories Built up From Observations. The Inductivist Ideal.” Before launching into the different philosophical approaches, Berson asks three questions about Theory. What is it? Why do we need it? Where does it come from?

I liked how Berson delved into the etymology of the word “theory”. Apparently its Greek antecedents, theoria and theorein, mean a “spectacle or speculation” and “to look at” and that these derive from theos meaning “god”. Since one of my chemistry classes is part of a live-and-learn community with the theme “Faith and Reason”, this made me think about how a religiously faithful scientist might characterize the activity of a scientist as “thinking God’s thoughts after Him” (which I think can be attributed to Saint Augustine). As an aside, my faculty colleagues in this community jokingly ask each other whether we have been faithful and reasonable in our endeavors, whatever they may be!

One of the things I try to get across to my students is that the colloquial use of the word “theory” is different from its use in science. “That’s just a theory!” implies something of possibly fanciful imagination. Theories in science are however much more substantial. Berson would say that “several levels of our knowledge of natural phenomena may [roughly] be identified with a set of raw observations, then a law, which expresses and codifies related observations into identifiable groups, and finally a theory that groups together or classifies related laws, explains why they are related and predicts new phenomena.” He goes on to say that “some theories are widely accepted and guide the thinking and action of most of the scientific community, some are accepted as probable, although acceptance may not be universal, some are speculative, and some, although currently accepted, are destined to be shown wrong.”

But why bother having a theory in the first place? Mach and Duhem thought that one purpose is to achieve an “economy of thought”. Poincare is quoted again. “Thanks to generalization, each fact observed enables us to foresee a great many others.” In this sense, Berson summarizes that “the creation and testing of theories lie at the core of science and define its program. In this sense, the experimentalist treasures theory as the source of inspiration for new investigations.” Berson then goes on to describe key figures in the school of inductivism, Popper’s hardline falsification approach, the more pragmatic approach (in my opinion) of Lakatos and colleagues, and the “anything goes” of Feyerabend. The philosophically inclined will find Berson’s book interesting particularly if they are organic chemists. (If you’re not a chemist, the examples can be dense.) Berson provides plenty of examples in the field of organic chemistry, not something you see in most discussions in philosophy of science, where if any chemistry is represented it is typically physical chemistry.

I want to return back to Hoffman for a moment. In a 2007 article of the journal Synthese, he has a paper titled “What might philosophy of science look like if chemists built it?” The main point is to investigate what makes chemistry different and unique, when compared to the other sciences. In particular, Hoffmann argues against simplistic reductionism, an idea he says is “alive and well within science”. He divides understanding into vertical and horizontal components. While the vertical is classical reductionism, “horizontal understanding is expressed in the concepts, definitions, and symbolic structures at the same level of complexity as the object to be understood. Horizontal explanations, like dictionary definitions, but richer, are quasi-circular. And none the worse for it.”

Hoffmann lists some productive concepts in chemistry that are not easily reducible to physics: “aromaticity, the acid-base concept, the idea of a functional group, a substituent effect, and that of a chromophore. And let us not forget the chemical bond.” This made me think of the rather ubiquitous use of electronegativity for all sorts of chemical explanations in a first year college chemistry class. I try to impress on my students the quasi-empirical nature of using the Pauling values although I’m not sure they really understand this. When I teach inorganic chemistry, we look more carefully at the Mulliken values, the Allred values and discuss how the Periodic Table might even be arranged differently! That’s another example of a model that is not easily reducible: While the Periodic Table systematizes some aspects of chemistry, to me it is a reminder of the uniqueness and seemingly idiosyncratic nature of each element, pulled together in a “theory” represented by a two-dimensional model. It is interesting and very useful, but is it “true”? And that’s why it behooves me to think a little more carefully about the philosophy of chemistry.

(I recommend Hoffmann’s articles. They are relatively easy to read and follow along even if you are not a chemist. But you will particularly enjoy them if you are a chemist!)