axocanth:
The scientific method is often called this, that, and the other. Hypothetico-deductivism is just one of many things that it is called, and like all the other suggestions (e.g. inductivism), it comes with problems galore.
All labels and descriptions come with problems galore if you want to go looking for them. This is something that certain philosophers love to spend lots of time on. (Not judging, just saying. Good luck to them.)
Newton, for example, did not see himself as following the H-D method, indeed he and other inductivists (common at the time) explicitly expresses contempt for hypotheses: they have no place in good science!
I'm not really aware of how well developed these kinds of categories and descriptions were in the 1600s. At that time, "science" itself was only starting to be clearly distinguished from other kinds of intellectual pursuits. "Natural philosophy" was a thing - it's in the title of Newton's most famous book - but "physics" wasn't, exactly.
Newton spent a lot of his time trying to "decode" the bible and trying to turn lead into gold, neither of which is well regarded in scientific circles today.
In other words, I'm not sure we should be over-reliant on Newton's opinion when it comes to what makes for good scientific method.
The hypothetico-deductive method, as commonly understood, at least as I understand it, is a method for testing scientific theories, not for their construction. Again, as typically formulated, it offers no advice whatsoever on how to construct a theory. Rather, it tells you what to do once you have a theory (see top of this post again).
Einstein tells us explicitly time and time again that, in general, there is no logic or method for the construction of a physical theory and, in particular, that he himself did not follow any logic or method in the construction of general relativity. E.g.
"I have learned something else from the theory of gravitation. No ever so inclusive collection of empirical facts can ever lead to the setting up of complicated equations. A theory can be tested by experience, but there is no way from the experience to the setting up of a theory"
The H-D "method" can 'begin' at different points in the 'cycle', which is really more of feedback loop. You can start with experience/observation, then formulate a hypothesis/theory, then test the theory, then tweak the theory based on the results. Or you can start with a hypothesis/theory, then test the theory, then adjust, then observe some more, and so on. This is a continually iterative loop, no matter where it starts.
Einstein is correct that to formulate a hypothesis/theory, one needs to start with an
idea about what
might be true (or false). That's a creative process.
Seeing an apple fall off a tree does not inevitably lead to a theory of gravity. It takes an Isaac Newton to have an idea and to ask the right kinds of questions before anything further can happen. As for "complicated equations", mathematics is considered by many scientists to be a
tool. While some scientific theories start with ideas that come from mathematical insights, I think that more often the mathematical insights come after the initial spark of an idea or the realisation that there is a question that seems to need an answer.
BTW, it's very popular these days for people who don't know much science - especially on the internet - to quote Einstein as saying "Imagination is more important than knowledge". The unexpressed hope of the lazy internet pundit is that they will be able to get away without needing knowledge - that they will get by on imagination alone. They hope in vain. Einstein didn't
just have imagination; he also had lots of knowledge, experience and hard-earned expertise.
Some questions then:
Q1: You are evidently telling us -- his own repeated denials to the contrary notwithstanding -- that Einstein was following a method in the construction of GR. Is this your view? Proceeding on that assumption (ignore the following questions otherwise) . . .
In broad brushstrokes, yes, Einstein was following the "scientific method". He studied certain aspects of nature in intimate detail. He had some ideas, which led him to formulate some "what if?" questions. He then drew on his expertise (or, in some case, went out and learned new stuff until he was an expert) to express his ideas and questions in the "language" of science - i.e. to formulate testable hypotheses and to make quantitative predictions about certain observations. Later - in some cases, much later - other scientists tested Einstein's hypotheses and found that his predictions were a better match to observations/experimental results than the predictions of various competing theories (e.g. Newtonian physics).
On the other hand, you seem to be looking for a "nitty gritty" method, so that we can say "Step 1 in The Scientific Method is to ... Then we move on to Step 2, in which we ..." and so on, like a recipe. I'm not saying Einstein followed a step-by-step recipe that anybody could have followed that would have inevitably led to the General Theory of Relativity. Science doesn't work like that. However, a
lot of scientists will tell you that they believe that if Einstein hadn't "discovered" his general theory, somebody else would have, sooner or later. That's partly because the General Theory is not a
purely creative act of imagination by one man. Einstein stood on the shoulders of giants, as was said of Newton. Science is cumulative. Science is communal. Science is social. It's not a mindless process of following a set of instructions.
I believe I have answered your Q2 and half of Q3 above.
Q3: ... What method do scientists in general, and Einstein in particular, use to construct their theories?
If you're looking for a no-brainer recipe with a set of steps that any idiot would only have to follow to arrive at General Relativity, I guess that, in principle, a set of steps
could be written down for that specific example. Obviously Einstein himself went through a series of steps and got to the end. If he could do it, other people can too. (People can be
taught about specific scientific theories and how they were developed.)
That's a very low, workmanlike level of specificity for what one might want in terms of a blueprint for constructing a theory. What
you are asking for, I think, is a
general method for constructing theories
about anything (or about anything scientific). I guess that I could start to write down a recipe for such a thing for you, too, but I don't know how helpful it would be in terms of giving you specific advice. It might go something like this (not necessarily in this order):
1. Go outside and observe a natural phenomenon.
2. Come up with a question like "Why does it do that?" or "How did that thing come to be the way it is?" or "What would be a good description of how thing X does action Y, which might be more generally applicable to things other than X?"
3. Take some science courses. Learn what our best current scientific theories have to say regarding the phenomenon of interest.
4. Using your acquired expertise, imagine a plausible answer to your question from step 2.
5. Using your acquired scientific skills, formulate a testable hypothesis - preferably quantitative - that can be used to check whether your answer in step 4 is wrong or right.
6. Flesh out any necessary details required to make meaningful predictions from your "theory" or hypothesis.
7. Test the hypothesis experimentally/observationally, or get somebody else to do it for you.
8. Analyse the results.
9. Compare the results to what your hypothesis predicted. Note any discrepancies between theory and observation carefully.
10. Repeat from step 2.
You will notice that there's nothing explicit here about how to learn tensor calculus, or about why curved spacetime might be a good basis for a theory of gravity. Nothing in this list would point Einstein specifically in the "right" direction to get to General Relativity, specifically. But that's not a problem. You asked for a general method, so I've given you a general method.
Just for comparison, I think this is a bit like asking "Can you give me a general method for writing a symphony? If you can't, then I say there's no such thing as a so-called Musical Method! Game Over! You lose!" But is that true? Are symphonies a product of the purely creative human mind, or is How to Write a Symphony something that somebody can be taught? Can we meaningfully provide some guidelines about better and worse ways to go about writing a symphony? I say we can. I also say this isn't so different from the position with science.
There are better and worse ways to go about doing science that can be taught and learned. It's not random. It's not a "methodless" enterprise. If there was no "method" to it, then taking a science course would be a waste of time in terms of preparing a person for the job of "scientist". At best, it would just be an exercise in rote memorisation of a bunch of "facts" that were arrived at by other people more or less by accident or at random, I suppose due to freakish accidents of imagination.