There’ll be a much more detailed post shortly about Wesley Salmon’s ‘statistical-relevance’ theory of scientific explanation (a response and extension from Hempel’s ‘deductive-nomological’ and ‘inductive-stastical’ approaches, discussed in an earlier post). In the mean time, though, a quick discussion on realism and anti-realism.
The distinction is that realists accept that the unobservable entities that we use in our scientific explanations such as fields, atoms, electrons, photons and so on are real features of the universe. Anti-realists – and one prominent school within this camp is the instrumentalists – claim that these entities are useful rather than true. They serve their purpose in that they help us to provide explanations that work and theories that allow us to describe and predict observable phenomena, but they are not considered to be in any sense ‘real’. Hempel is an anti-realist, and constructs scientific explanations in terms of logical relations and laws. Salmon, on the other hand, is a realist1.
As a side note, Bas van Fraassen, another important figure in the philosophy of explanation (who, for various reasons, I will mention only in passing in my book) describes his position as ‘constructive empiricism’. While the anti-realist is an ‘atheist’ in terms of unobservable entities and makes the strong claim that they are not real, a constructive empiricist is ‘agnostic’: s/he neither knows nor cares whether they exist, and their reality is not a required feature of the approaches to explanation proposed by van Fraassen and those who follow him.
Salmon essentially uses two arguments in support of the reality of the unobservable. The first relates to extending the range of our senses. He talks about what he can see in a book with tiny print with and without his glasses, and notes that it would seem very odd to claim that the full stops on the page are not real when he has his glasses off but are real when he has his glasses on and can observe them. He then extends this, noting that the optics of a microscope are based on the exact same principles as the optics used in making his glasses, so it makes sense to consider the things that can be observed through a microscope to be real.
The argument then extends to telescopes and things like the moons of the planets in our solar system, which are not visible to the naked eye. The objection has been made by others that we could, in principle, travel to the moons of the planets and verify their existence with our senses but that we can’t (‘Fantastic Voyage’ aside) travel to the microscopic realm to check our observations in the same way.
In response to this, Salmon talks about a process by which a grid is designed at macroscale then shrunk and manufactured at microscopic scale and used for things like counting bacteria in a sample under a microscope. It seems quite silly to claim that, at the scale when we can no longer observe it directly with our unaided senses, such a grid loses its reality.
The final argument is based on the work of Jean Perrin, who started out observing Brownian motion (the way in which very small particles suspended in a fluid (gas or liquid) exhibit random movement, which is explained as being caused by collisions with the particles in the fluid, e.g. water molecules or nitrogen molecules in air). Brownian motion allows the direct observation (though usually aided by a microscope, because particles small enough to be bumped off course by a single molecule are pretty small) of the effects of molecules, although the molecules themselves cannot be seen. Perrin used Brownian motion to find the value of Avogadro’s Number, 6.02 x 1023, a very important number in chemistry that relates the molecular and macro scales.
The really interesting thing, though, is that Perrin then went on to find 13 different and independent ways to determine the value of Avogadro’s number, such as electroplating silver out of a solution and measuring the current used for a given mass of silver, radioactive decays and so on. The fact that a range of independent experiments, across a range of different branches of chemistry and physics, all yielded the same number (within experimental error) is at least pretty strong inferential empirical evidence for the reality of atoms, molecules and electrons.
When we get to photons and other entities at the level where quantum phenomena are dominant, it gets more complex still… things sometimes behave like particles and sometimes like waves. Are they ‘real’? They help us to create good – if complex (literally) – explanations.
I have to admit that, while in general I’m probably inclined toward realism, if I had to swear to it, hand on heart, constructive empiricism would be an attractive approach for me. Or is that just a copout?
There’s a good, if somewhat technical, introduction to some of the issues in explanation here: https://www.iep.utm.edu/explanat/ For me, it makes too much of the implications of this realist/anti-realist distinction, when I find other aspects of explanation more interesting and important, but nonetheless it does a nice job of sketching the last 70 years in the philosophy of this issue, since Hempel and Oppenheim’s seminal paper in 1948.
More Salmon shortly.
- Like many other terms in science and philosophy, ‘realist’ has a technical and an everyday meaning. In everyday parlance, a ‘realist’ is someone who takes the world as it is, as opposed to an ‘idealist’ who seeks to work as though the world follows – or ought to follow – some ideal order. It’s important to distinguish that sense of the term ‘realist’ from the technical meaning discussed in this post.