The so-called "scientific method" is, I think, rather poorly understood. For example, let us consider one of the best-known laws of nature, often simply referred to as the Law of Gravity:
Newton's Law of Universal Gravitation: Every object in the universe attracts every other object toward it with a force proportional to the product of their masses, divided by the square of the distance between their centers of mass.
Now here is a series of questions for you, which I often ask audiences when I give lectures on the philosophy of science:
- Do you believe Newton's Law of Universal Gravitation is true?
- If so, how sure are you that it is true?
- Why do you believe it, with that degree of certainty?
The most common answers to these questions are "yes", "very sure", and "because it has been extensively experimentally verified." Those answers sound reasonable to any child of the Enlightenment -- but I submit, on the contrary, that this set of answers has no objective basis whatsoever. To begin with, let us ask, how many confirming experiments do you think would have been done, to qualify as "extensive experimental verification." I would ask that you, the reader, actually pick a number as a rough, round guess.
Whatever number N you picked, I now challenge you state the rule of inference that allows you to conclude, from N uniform observations, that a given effect is always about from a given alleged cause. If you dust off your stats book and thumb through it, you will find no such rule of inference rule there. What you will find are principles that allow you to conclude from a certain number N of observations that with confidence c, the proportion of positive cases is z, where c < 1 and z < 1. But there is no finite number of observations that would justify, with any nonzero confidence, that any law held universally, without exception (that is, z can never be 1 for any finite number of observations, no matter how small the desired confidence c is, unless c = 0). . And isn't that exactly what laws of nature are supposed to do? For Pete's sake it is called the law of universal gravitation, and it begins with the universal quantifier every (both of which may have seemed pretty innocuous up until now).
Let me repeat myself for clarity: I am not saying that there is no statistical law that would allow you to conclude the law with absolute certainty; absolute certainty is not even on the table. I am saying that there is no statistical law that would justify belief in the law of universal gravitation with even one tenth of one percent of one percent confidence, based on any finite number of observations. My point is that the laws of the physical sciences -- laws like the Ideal gas laws, the laws of gravity, Ohm's law, etc. -- are not based on statistical reasoning and could never be based on statistical reasoning, if they are supposed, with any confidence whatsoever, to hold universally.
So, if the scientific method is not based on the laws of statistics, what is it based on? In fact it is based on the
Principle of Abductive Inference: Given general principle as a hypothesis, if we have tried to experimentally disprove the hypothesis, with no disconfirming experiments, then we may infer that it is likely to be true -- with confidence justified by the ingenuity and diligence that has been exercised in attempting to disprove it.
In layman's terms, if we have tried to find and/or manufacture counterexamples to a hypothesis, extensively and cleverly, and found none, then we should be surprised if we then find a counterexample by accident. That is the essence of the scientific method that underpins most of the corpus of the physical sciences. Note that it is not statistical in nature. The methods of statistics are very different, in that they rest on theorems that justify confidence in those methods, under assumptions corresponding to the premises of the theorems. There is no such theorem for the Principle of Abductive Inference -- nor will there ever be, because, in fact, for reasons I will explain below, it is a miracle that the scientific method works (if it works).
Why would it take a miracle for the scientific method to work? Remember that the confidence with which we are entitled to infer a natural law is a function of the capability and diligence we have exercised in trying to disprove it. Thus, to conclude a general law with some moderate degree of confidence (say, 75%), we must have done due diligence in trying to disprove it, to the degree necessary to justify that level confidence, given the complexity of the system under study. But what in the world entitles us to think that the source code of the universe is so neat and simple, and its human denizens so smart, that we are capable of the diligence that is due?
For an illuminating analogy, consider that software testing is a process of experimentation that is closely analogous to scientific experimentation. In the case of software testing, the hypothesis being tested -- the general law that we are attempting to disconfirm -- is that a given program satisfies its specification for all inputs. Now do you suppose that we could effectively debug Microsoft Office, or gain justified confidence in its correctness with respect to on item of its specification, by letting a weasel crawl around on the keyboard while the software is running, and observing the results? Of course not: the program is far too complex, its behavior too nuanced, and the weasel too dimwitted (no offense to weasels) for that. Now, do you expect the source code of the Universe itself to be simpler and friendlier to the human brain than the source code of MS Office is to the brain of a weasel? That would be a miraculous thing to expect, for the following reason: a priori, if the complexity of that source code could be arbitrarily large. It could be a googleplex lines of spaghetti code -- and that would be a infinitesimally small level of complexity, given the realm of possible complexities -- namely the right-hand side of the number line.
In this light, if the human brain is better equipped to discover the laws of nature than a weasel is to confidently establish the correctness an item in the spec of MS Office, it would be a stunning coincidence. That is looking at it from the side of the a priori expected complexity of the problem, compared to any finite being's ability to solve it. But there is another side to look from, which is the side of the distribution of intelligence levels of the potential problem-solvers themselves. Obviously, a paramecium, for example, is not equipped to discover the laws of physics. Nor is an octopus, nor a turtle, nor a panther, nor an orangutan. In the spectrum of natural intelligences we know of, it just so happens that there is exactly one kind of creature that just barely has the capacity to uncover the laws of nature. It is as if some cosmic Dungeon Master was optimizing the problem from both sides, by making the source code of the universe just simple enough that the smartest beings within it (that we know of) were just barely capable of solving the puzzle. That is just the goldilocks situation that good DM's try to achieve with their puzzles: not so hard they can't be solved, not so easy that the players can't take pride in solving them
There is a salient counterargument I must respond to. It might be argued that, while it is a priori unlikely that any finite being would be capable of profitably employing the scientific method in a randomly constructed universe, it might be claimed that in hindsight of the scientific method having worked for us in this particular universe, we are now entitled, a posteriori, to embrace the Principle of Abductive Inference as a reliable method. My response is that we have no objective reason whatsoever to believe the scientific method has worked in hindsight -- at least not for the purpose of discovering universal laws of nature! I will grant that we have had pretty good luck with science-based engineering in the tiny little spec of the universe observable to us. I will even grant that this justifies the continued use of engineering for practical purposes with relative confidence -- under the laws of statistics, so long as, say, one anomaly per hundred thousand hours of use is an acceptable risk. But this gives no objective reason whatsoever (again under the laws of statistics) to believe that any of the alleged "laws of nature" we talk about is actually a universal law. That is to say, if you believe, with even one percent confidence, that we ever have, or ever will, uncover a single line of the source code of the universe -- a single law of Nature that holds without exception -- then you, my friend, believe in miracles. There is no reason to expect the scientific method to work, and good reason to expect it not to work -- unless human mind was designed to be able to uncover and understand the laws of nature, by Someone who knew exactly how complex they are.
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Notes -
Sure, Popper is developing the idea of degree of corroboration in that book, so he mentions it a lot. But no degree of corroboration can change the epistemic status of a theory, which always remains a conjecture. Like I said, it's a common mistake, and Popper shares some of the blame for by speaking about "preference" in the context of corroboration, which sounds a lot like justification or that we "rationally ought" to believe the better tested theory as if it had a greater likelihood of being true, or something like that. Popper did a lot to muddle the waters here. But corroboration is a measure of the state of the critical discussion, and not in any way a measure of the justification, reliability, probability, etc. of a theory. With regard to the epistemic status of a theory being adjusted by evidence, which is what is relevant to our discussion, corroboration does nothing. Here's Popper saying it outright, in Objective Knowledge 1972 (1979 revised edition), p. 18:
As the missile example:
This would be my conjecture, motivated in part by how poorly tested quantum computing is, but not justified or "based" on that. It's my best guess that has taken into consideration the evaluation of the state of the critical discussion on quantum computing (how well corroborated it is), but is not justified by it and remains a guess/conjecture. We can certainly take the degree of corroboration into consideration when deciding what to believe, but it can never elevate our beliefs beyond the status of conjecture, and it is in this epistemological sense that corroborating evidence does nothing.
I think I see now why I, like many people, misread Popper. Frankly, I think the position he expresses here is so egg-headed that I did not anticipate it. He implicitly conditions future performance (aka reliability) on justified confidence in general, literal truth, and so winds up concluding that theories of physical world have only two levels of reliability: known false, and other. This position hamstrings his theory of corroboration with respect to establishing a rational basis for action -- and that moves him to the bottom of my reading list for philosophy of science. It's not that his work has no intellectual merit (it's all very interesting); it's just that I have better things to do, because I am interested science as a rational basis for discriminating between alternative courses of action, and in philosophy of science as an articulated theory of the rules of evidence for doing so.
It appears that Popper (1) accepts the essence of my argument in the original post, but (2) doesn't believe in miracles -- which commits him to his position on reliability and future-performance, and also makes his theory of corroboration impotent a basis for rational action. I share his view of (1) but not (2).
For clarity, do you agree with the Popper on this (that corroboration says nothing whatever about the future performance of a theory)?
Yup, you got it. There's no establishing a rational basis for action, it cannot be done. You have done a good job articulating some of the obstacles to this in your original post. We can, however, still use reason and logic in the method of eliminating errors in the pursuit of truth. That's Popper's insight.
A small note: there is no "known false" category. Falsification is not justified either, it is as conjectural as anything else. So yes, justification doesn't work, and there is no rational basis to be had. But we can still engage in the rational pursuit of truth, in the sense of using reason and experience to temper our conjectures about the world.
As for your future reading, go with your interests, of course, but I can still recommend this short article articulating this position: https://www.science.org/doi/10.1126/science.284.5420.1625
The beauty and clarity of Popper's view is relinquishing justification and the search for a "basis", which reason and rationality are not capable of providing, but still maintaining rationality, empiricism, and the pursuit of truth. It's worth keeping in mind at least, as a possible different path that eschews the use of justification and "good reasons" but retains the use of reason and truth as the aim of science. If ever you stop believing in miracles, you need not despair of reason just yet, give Popper's view a shot first :)
I'll leave you with a final Popper quote:
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