According to most treatments of philosophy of science, or at least most of those that I have looked at, science advances by means of inductive generalizations. Inductive generalizations are often assumed to be the basis for scientific laws (such as laws of physics).
To me, that seems wrong. I do not see the evidence that science is using induction.
I can agree that there are generalizations in science. But it does not seem to me that they are inductive generalizations.
Induction
First an example of induction, to illustrate what is meant by the term.
All the many crows that I have seen are black. Therefore all crows are black.
This example is similar to typical examples from philosophy of science. Doubtless, it is intentionally oversimplified and exaggerated, so as to more readily communicate the idea. So we should not assume that this is intended as a literal example of how science is said to work.
I should mention that there is a method called “Baconian induction“, which is different from philosophical induction, and perhaps closer to what science actually uses. But Baconian induction is rarely mentioned by philosophers of science.
Induction has long been subject to skeptical criticism. The main skeptical objection, is that induction is not logically valid. However, others have suggested that induction is still rational, even if not logically valid.
It seems to me that it would require miracles for induction to be the basis of scientific laws. Put crudely, induction would require that we make many observations (say, thousands). And then we compute an average (perhaps an average trend line). We then throw away all of the observations, and keep only that trend line, which we call a law. And, somehow, this is supposed to be far more useful than the original observations. It doesn’t make sense.
Predictions
Here’s an alternative that seems more plausible than induction.
All the many crows that I have seen are black. Therefore, I predict that the next crow that I see will be black.
This seems more plausible for several reasons. For one thing, it does not make a general claim (“all crows are black”). Instead, it limits itself to a specific claim (“the next crow that I see will be black”). Moreover, we don’t expect predictions to be perfect. If our predictions are better than pure guesses, then they already have some use to us. So a prediction is weaker than a claim of truth. And it doesn’t surprise us if we get some of our predictions wrong.
Perhaps if we worded induction in terms of predictions, that would make more sense. I’ll look at examples of that later in this post.
Newton’s laws
How did we get to Newton’s laws of motion? Some would have us believe that they result from induction. I can agree that they are some kind of generalization. But, to me, they look more like the kind of generalization that is used in mathematics, as discussed in my previous post. And if that’s the kind of generalization that was used, then it isn’t at all like induction.
At the time of Newton, the concept of force would mainly have been with the force required to raise heavy objects, or the force from using levers. Newton’s was pretty much the description of how weighing machine work, with the acceleration
being the acceleration due to gravity and the force
being the lifting force needed to oppose that acceleration. What Newton’s laws achieved, was to generalize the concept of force, so that we could then talk of, for example, the force of friction and the force of air resistance. And not only could we talk of them, but
gave us a way to measure those forces, as long as we could measure the acceleration. It seems to me that Newton’s laws were effective, mainly because they increased what we could measure and thus increased the amount of data available to use in making predictions.
Conductivity of copper
Here’s an example that looks closer to the traditional description of induction. Scientists measure the electrical conductivity of a few sample of copper. And then they publish this in a reference table that can be widely consulted. So it looks as if they took a few measurements, and generalized from that.
That seems fair enough. And you can call that “induction” if you like. But why does it work? The reason is because copper is known to be a very homogeneous material, so that the conductivity should be the same for all samples.
The real work here isn’t in the induction. Rather, it is in the purification processes that give us a very homogeneous copper. And part of that is in the way that the scientists carve up the world into different objects and different materials. The highly systematic way in which scientists carve up and organize the world is a very important in why science works as well as it does.
For that matter, the way we organize the world has a lot to do with other proposed inductions. Suppose somebody argued:
All the many birds that I have seen are black. Therefore all birds are black.
Such an argument would be seen as absurd. But when specified for crows, it seems more plausible. And, again, the difference is that crows are a fairly homogeneous group. Note, though, that a similar argument about parrots would seem absurd, because the varied coloring is a characteristic of parrots.
Kepler’s laws
Kepler did use data on observations of planets. And he apparently plotted those and looked for a trend line. You do not get an exact ellipse by joining plotted points in a graph. It is likely that Kepler picked the ellipse for its mathematical simplicity and because its shape seemed roughly similar to the planetary plots. And then he fitted ellipses to the plotted data. As I have posted previously, Kepler’s laws are false. And it must have been obvious to Kepler that they are false. That is to say, it must have been obvious that his plotted points did not exactly fit on the ellipses. To me, it seems likely that Kepler was mainly concerned about the ability to predict. If he could come up with curves that fitted well, if imperfectly, and that were mathematically tractable, then he could use those curves to make reasonably accurate predictions of planetary motion.
As it happened, Newton was able to derive Kepler’s laws in his mathematical solution for the two-body problem. So Kepler’s choice of the ellipse was particularly fortuitous.
Boyle’s law, Ohm’s law
It seems almost certain that Boyle knew his law was false, though a very useful approximation. And I am inclined to think that Ohm probably knew that his law was false, though a good approximation. In both cases, we have laws that are useful for making good approximations, though not strictly true. At least, as typically described by philosophers, induction is supposed to yield truth. I suggest it would be better to describe these laws as pragmatic conventions which have proved of value in making predictions.
Summary
Scientific theories and scientific laws are varied. They cannot all be described in the same way. It seems to me that induction is never a good description of what science does. I’ve given some examples of laws that I would describe as pragmatic conventions that have been shown to make useful predictions. And some laws and theories appear to be more like the kind of generalization that we see in mathematics. I’ve mentioned Newton’s laws as an example of this. Einstein’s general theory of relativity is another example.