Infinite regresses are nasty problems for epistemologies.
All justificationist epistemologies have an infinite regress.
That means they are false. They don't work. End of story.
There are options of course. Don't want a regress? No problem. Have an arbitrary foundation. Have an unjustified proposition. Have a circular argument. Or have something else even sillier.
The regress goes like this, and the details of the justification don't matter.
If you want to justify a theory, T0, you have to justify it with another theory, T1. Then T1 needs justifying by T2. Which needs justifying by T3. Forever. And if T25 turns out wrong, then T24 loses it's justification. And with T24 unjustified, T23 loses its justification. And it cascades all the way back to the start.
I'll give one more example. Consider probabilistic justification. You assign T0 a probability, say 99.999%. Never mind how or why, the probability people aren't big on explanations like that. Just do your best. It doesn't matter. Moving on, what we should wonder is if that 99.999% figure is correct. If it's not correct then it could be anything such as 90% or 1% or whatever. So it better be correct. So we better justify that it's a good theory. How? Simple. We'll use our whim to assign the probability estimate itself a probability of 99.99999%. OK! Now we're getting somewhere. I put a lot of 9s so we're almost certain to be correct! Except, what if I had that figure wrong? If it's wrong it could be anything such as 2% or 0.0001%. Uh oh. I better justify my second probability estimate. How? Well we're trying to defend this probabilistic justification method. Let's not give up yet and do something totally differently, instead we'll give it another probability. How about 80%? OK! Next I ask: is that 80% figure correct? If it's not correct, the probability could be anything, such as 5%. So we better justify it. So it goes on and on forever. Now there's two problems. First it goes forever, and you can't ever stop, you've got an infinite regress. Second, suppose you stopped after some very large but finite number of steps. Then the probability the first theory is correct is arbitrarily small. Because remember that at each step we didn't even have a guarantee, only a high probability. And if you roll the dice a lot of times, even with very good odds, eventually you lose. And you only have to lose once for the whole thing to fail.
OK so regresses are a nasty problem. They totally ruin all justificationist epistemologies. That's basically every epistemology anyone cares about except skepticism and Popperian epistemology. And forget about skepticism, that's more of an anti-epistemology than an epistemology: skepticism consists of giving up on knowledge.
So how could Popperian epistemology deal with regresses?(I've improved on Popper some.)
Regresses all go away if we drop justification. Don't justify anything, ever. Simple.
But justification had a purpose.
The purpose of justification is to sort out good ideas from bad ideas. How do we know which ideas are any good? Which should we believe are true? Which should we act on?
BTW that's the same general problem that induction was trying to address. And induction is false. So that's another reason we need a solution to this issue.
The method of addressing this issue has several steps, so try to follow along.
Step 1) You can suggest any ideas you want. There's no rules, just anything you have the slightest suspicion might be useful. The source of the ideas, and the method of coming up with them, doesn't matter to anything. This part is easy.
Step 2) You can criticize any idea you want. There's no rules again. If you don't understand it, that's a criticism -- it should have been easier to understand. If you find it confusing, that's a criticism -- it should have been clearer. If you think you see something wrong with it, that's a criticism -- it shouldn't have been wrong in that way, *or* it should have included an explanation so you wouldn't make a mistaken criticism. This step is easy too.
Step 3) All criticized ideas are rejected. They're flawed. They're not good enough. Let's do better. This is easy too. Only the *exact* ideas criticized are rejected. Any idea with at least one difference is deemed a new idea. It's OK to suggest new ideas which are similar to old ideas (in fact it's a good idea: when you find something wrong with an idea you should try to work out a way to change it so it won't have that flaw anymore).
Step 4) If we have exactly one idea remaining to address some problem or question, and no one wants to revisit the previous steps at this time, then we're done for now (you can always change your mind and go back to the previous steps later if you want to). Use that idea. Why? Because it's the only one. It has no rivals, no known alternatives. It stands alone as the only non-refuted idea. We have sorted out the good ideas from the bad -- as best we know how -- and come to a definite answer, so use that answer. This step is easy too!
Step 5) What if we have a different number of ideas left over which is not exactly one? We'll divide that into two cases:
Case 1) What if we have two or more ideas? This one is easy. There is a particular criticism you can use to refute all the remaining theories. It's the same every time so there's not much to remember. It goes like this: idea A ought to tell me why B and C and D are wrong. If it doesn't, it could be better! So that's a flaw. Bye bye A. On to idea B: if B is so great, why hasn't it explained to me what's wrong with A, C and D? Sorry B, you didn't answer all my questions, you're not good enough. Then we come to idea C and we complain that it should have been more help and it wasn't. And D is gone too since it didn't settle the matter either. And that's it. Each idea should have settled the matter by giving us criticisms of all its rivals. They didn't. So they lose. So whenever there is a stalemate or a tie with two or more ideas then they all fail.
Case 2) What if we have zero ideas? This is crucial because case one always turns into this! The answer comes in two main parts. The first part is: think of more ideas. I know, I know, that sounds hard. What if you get stuck? But the second part makes it easier. And you can use the second part over and over and it keeps making it easier every time. So you just use the second part until it's easy enough, then you think of more ideas when you can. And that's all there is to it.
OK so the second part is this: be less ambitious. You might worry: but what about advanced science with its cutting edge breakthroughs? Well, this part is optional. If you can wait for an answer, don't do it. If there's no hurry, then work on the other steps more. Make more guesses and think of more criticisms and thus learn more and improve your knowledge. It might not be easy, but hey, the problem we were looking at is how to sort out good ideas from bad ideas. If you want to solve hard problems then it's not easy. Sorry. But you've got a method, just keep at it.
But if you have a decision to make then you need an answer now so you can make your decision. So in that case, if you actually want to reach a state of having exactly one theory which you can use now, then the trick is when you get stuck be less ambitious. How would that work in general terms? Basically if human knowledge isn't good enough to give you an answer of a certain quality right now, then your choices are either to work on it more and not have an answer now, or accept a lower quality answer. You can see why there isn't really any way around that. There's no magic way to always get a top quality answer now. If you want a cure for cancer, well I can't tell you how to come up with one in the next five minutes, sorry.
This is a bit vague so far. How does lowering your standards address the problem? So what you do is propose a new idea like this, "I need to do something, so I will do..." and then you put whatever you want (idea A, idea B, some combination, whatever else).
This new idea is not refuted by any of the existing criticisms. So now you have one idea, it isn't refuted, and you might be done. If you're happy with it, great. But you might not be. Maybe you see something wrong with it, or you have another proposal. That's fine; just go back to the first three steps and do them more. Then you'll get to step 4 or 5 again.
What if we get back here? What do we do the second time? The third time? We simply get less ambitious each time. The harder a time we're having, the less we should expect. And so we can start criticizing any ideas that aim too high (while under too much time pressure to aim that high).
BTW it's explained on my website here, including an example:
Read that essay, keeping in mind what what I've been saying, and hopefully everything will click. Just bear in mind that when it talks about cooperation between people, and disagreements between people, and coming up with solutions for people -- when it discusses ideas in two or more separate minds -- everything applies exactly the same if the two or more conflicting ideas are all in the same mind.
What if you get really stuck? Well why not do the first thing that pops into your head? You don't want to? Why not? Got a criticism of it? It's better than nothing, right? No? If it's not better than nothing, do nothing! You think it's silly or dumb? Well so what? If it's the best idea you have then it doesn't matter if it's dumb. You can't magically instantly become super smart. You have to use your best idea even if you'd like to have better ideas.
Now you may be wondering whether this approach is truth-seeking. It is, but it doesn't always find the truth immediately. If you want a resolution to a question immediately then its quality cannot exceed today's knowledge (plus whatever you can learn in the time allotted). It can't do better than the best that is known how to do. But as far as long term progress, the truth seeking came in those first three steps. You come up with ideas. You criticize those ideas. Thereby you eliminate flaws. Every time you find a mistake and point it out you are making progress towards the truth; you're learning. That's how we approach the truth: not by justifying but by identifying mistakes and learning better. This is evolution, it's the solution to Paley's problem, it's discussed in BoI and on my Fallible Ideas website. And it's not too hard to understand: improve stuff, keep at it, and you make progress. Mistake correcting -- criticism -- is a truth-seeking method. That's where the truth-seeking comes from.