Okay, I don't know why everyone is making this so complicated.
In theory, nothing is presupposed. We aren't certain of anything and never will be.
In practice, if induction works for you (it will) then use it! Once it's just a question of practicality, try anything you like, and use what works.
It won't let you be certain, but it'll let you move with power within the world.
As for values, morals, your question suggests you might be interested in A Thousand Shards of Desire in the sequences. We value what we do, with lots of similarities to each other, because evolution designed our psychology that way.
Evolution is messy and uncoordinated. We ended up with a lump of half random values not at all coherent.
So, we don't look for, or recommend looking for, any One Great Guiding Principle of morality; there probably isn't one.
We just care about life and fairness and happiness and fun and freedom and stuff like anyone else. Lots of lw people get a lot of mileage out of consequentialism, utilitarianism, and particularly preference utilitarianism.
But these are not presumed. Morality is, more or less, just a pile of things that humans value. You don't HAVE to prove it to get people to try to be happy or to like freedom (all else equal).
If I've erred here, I would much like to know. I puzzled over these questions myself and thought I understood them.
Having an official doctrine that nothing is certain is not a all the same as having no presuppositions. To have a presupposition is to treat something as true (including using it methodologically) without being able to prove it. In the absence of any p=1 data, it makes sense to use your highest probability uncertain beliefs presuppositionally. It's absence of foundations (combined with a willingness to employ it, nonetheless ) that makes something presuppositional, not presence of certainty.
Treating something as true non-methodologically means making infe...
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