P.S. Bayes Theorem is derived from a basic statement about conditional probability, such as the following:
P(S/T) = P(S&T)/P(T)
According to the SEP (http://plato.stanford.edu/entries/epistemology-bayesian/) this is usually taken as a “definition”, not an axiom, and Bayesians usually give conditional probability some real-world significance by adding a Principle of Conditionalization. In that case it’s the Principle of Conditionalization that requires justification in order to establish that Bayes Theorem is true in the sense that Bayesians require.
Just to follow up on the previous replies to this line of thought, see Wikipedia’s article on Cox’s theorem and especially reference 6 of that article.
On the Principle of Conditionalization, it might be argued that Cox’s theorem assumes it as a premise; the easiest way to derive it from more basic considerations is through a diachronic Dutch book argument.
P.S. Bayes Theorem is derived from a basic statement about conditional probability, such as the following:
P(S/T) = P(S&T)/P(T)
According to the SEP (http://plato.stanford.edu/entries/epistemology-bayesian/) this is usually taken as a “definition”, not an axiom, and Bayesians usually give conditional probability some real-world significance by adding a Principle of Conditionalization. In that case it’s the Principle of Conditionalization that requires justification in order to establish that Bayes Theorem is true in the sense that Bayesians require.
Just to follow up on the previous replies to this line of thought, see Wikipedia’s article on Cox’s theorem and especially reference 6 of that article.
On the Principle of Conditionalization, it might be argued that Cox’s theorem assumes it as a premise; the easiest way to derive it from more basic considerations is through a diachronic Dutch book argument.