5

In abduction we take some observations and try to find the hypothesis that best explains them.

In Bayesian terms this sounds like finding the Maximum A Posteriori (MAP) estimate. To a Bayesian, "best" means "most likely." If we combine this with a Minimum Description Length (MDL) prior distribution, then in Bayesian terms abduction seems to be the process of finding the shortest hypothesis that fully explains the data. Abduction is essentially just what Bayesian inference does, no more and no less.

Bayesian inference is also typically taken to be a model of induction. In Bayesian terms, induction is also a matter of finding the MAP estimate, which with a MDL prior would again be the shortest hypothesis that fully explains the data. It appears that abduction, Bayesian inference, and induction are all the same thing.

Is there any example of induction, or any example of abduction, that does not simply boil down to finding a MAP estimate?

What I see is that listed examples of induction typically focus on the formation of scientific theories, like the theory of gravity, whereas examples of abduction tend to focus on particular events, like figuring out where someone was last night. From a Bayesian perspective these two scenarios are treated in basically the same way. A Theory of Gravity is evaluated by how well it explains the data and how concise it is... and A Theory of Where You Were Last Night is also evaluated by how well it explains the data and how concise it is. If the focus on scientific theories vs the focus on particular events is the only real difference between induction and abduction, it seems arbitrary, when we can think about both kinds of things using the same tools (MAP estimation).

5
  • One can treat special cases of abduction in Bayesianism, but it does not make it expressible in Bayesian terms, let alone "the same thing". That those terms do not distinguish it from induction and reduce best to most likely are not good signs either. Your 'argument' is circular: "to a Bayesian" A is B, therefore, A is B "in Bayesian terms". Applications of abduction to theory building are easy to find. "It is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail" Maslow.
    – Conifold
    Commented Apr 20 at 10:23
  • Help! I've been abducted by Bayesians!
    – Scott Rowe
    Commented Apr 20 at 11:50
  • 1
    @Conifold "and reduce best to most likely..." are you saying you favor some interpretation of induction or abduction under which best is not most likely?
    – causative
    Commented Apr 20 at 15:45
  • So do you, "likely" may make no sense and "best" is judged on other grounds. Screws are not tightened with a hammer.
    – Conifold
    Commented Apr 21 at 0:48
  • @Conifold Under what circumstances would you say "likely" makes no sense and "best" is judged on other grounds? We always have subjective credences that allow us to talk about likelihood. Also, if someone favors a hypothesis even though honestly it's not the most likely, I think this would normally be pathological rather than ideal reasoning. For instance, favoring a hypothesis because it is popular or because of wishful thinking. (Technically in Bayesian inference we're not just concerned with MAP but with all hypotheses - we don't just pick one, though in many cases that's close enough.)
    – causative
    Commented Apr 21 at 0:56

0

You must log in to answer this question.

Browse other questions tagged .