One of the both frustrating and rewarding things about teaching physics is how much I have to work against the grain of everyday common sense thinking.
The obvious example is how almost everybody, unless they’re corrupted by having physics beat into their head for years on end, has an Aristotelian conception of force, inertia, and motion. But I also run into a more subtle obstacle. Most everyone has a quasi-Aristotelian conception of matter, of substance. And I run into traces of this not just among undergraduates, but in many common antimaterialist intuitions, often defended in sophisticated philosophical terms, that support the commonsense notion that there has to be an irreducibly mind-like principle at work in the universe and in our brains. After all, what is mere physics about, but material things? And what is matter, but blobs of substance that mix and collide with each other?
But such a conception can lead to all sorts of confusion, such as considering relationships between material objects as somehow separate from physical reality. Relationships become part of a shadowy Platonic plane of existence beyond the material. The math I put down on the blackboard becomes a glimpse of an immaterial essence; some principle that structures the otherwise shapeless blobs of substance that make up what we play with in the lab.
But to a physicist—someone brainwashed by having physics beat into their head for years on end—it makes no sense to talk about material objects, such as elementary particles, without their relationships. A photon or an electron is a bundle of properties that tell us how they interact. There is no “material substance” that remains after you strip away properties (charge, mass, spin, etc. etc.) that have meaning only in the context of interactions. If you’re talking about matter, you’re already talking about patterns and relations—inseparably, not as an attachment from a Platonic realm superimposed on shapeless blobs.
I sometime run into the accusation that materialists continue to rely on an outdated, 19th century conception of matter. Nonsense. Those of us inclined toward physicalism hold our views partly because we have a very 21st century conception of physical entities. The difficulty we often face is in explaining why. It becomes a hard task, since where most people’s intuitive ideas of matter are concerned, the 19th century would be a vast improvement. Whether we’re in the classroom or rolling our eyes at theistic philosophers, the quasi-Aristotelian “blobs of substance” picture is still an important obstacle we have to deal with.