Editing Subjectivism (section)

== In probability ==
Broadly speaking, there are two views on [[Bayesian probability]] that interpret the probability concept in different ways. In [[probability]], a subjectivist stand is the belief that probabilities are simply degrees-of-belief by rational agents in a certain proposition, and which have no objective reality in and of themselves. According to the subjectivist view, probability measures a "personal belief".<ref>[[Richard Threlkeld Cox|Cox, R. T.]] 2001. ''Algebra of Probable Inference'', The Johns Hopkins University Press. {{ISBN|978-0801869822}}</ref> For this kind of subjectivist, a phrase having to do with probability simply asserts the degree to which the subjective actor believes their assertion is true or false. As a consequence, a subjectivist has no problem with differing people giving different probabilities to an uncertain proposition, and all being correct.

Many modern machine learning methods are based on objectivist Bayesian principles.<ref>[[Christopher Bishop|Bishop, C.M.]] 2007. ''Pattern Recognition and Machine Learning''. Springer. {{ISBN|978-0387310732}}</ref> According to the objectivist view, the rules of [[Bayesian statistics]] can be justified by requirements of rationality and consistency and interpreted as an extension of logic.<ref>[[Edwin Thompson Jaynes|Jaynes, E.T.]] 1976. "Bayesian Methods: General Background", ''Maximum Entropy and Bayesian Methods in Applied Statistics'', by J. H. Justice (ed.). Cambridge: Cambridge Univ. Press. {{doi|10.1017/CBO9780511569678.003}}</ref><ref name="de Finetti">[[Bruno de Finetti|de Finetti, B.]] 1974. ''Theory of Probability'' (2 vols.), J. Wiley & Sons, Inc., New York). {{ISBN|978-0471201427}}</ref> In attempting to justify subjective probability, [[Bruno de Finetti]] created the notion of [[coherence (philosophical gambling strategy)|philosophical coherence]]. According to his theory, a probability assertion is akin to a bet, and a bet is coherent only if it does not expose the wagerer to loss if their opponent chooses wisely. To explain his meaning, de Finetti created a [[thought-experiment]] to illustrate the need for principles of coherency in making a probabilistic statement. In his scenario, when someone states their degree-of-belief in something, one places a small bet for or against that belief and specifies the odds, with the understanding that the ''other'' party to the bet may then decide which side of the bet to take. Thus, if Bob specifies 3-to-1 odds against a proposition A, his opponent Joe may then choose whether to require Bob to risk $1 in order to win $3 if proposition A is found to be true, or to require Bob to risk $3 in order to win $1 if the proposition A is not true. In this case, it is possible for Joe to win over Bob. According to de Finetti, then, this case is incoherent.<ref name="de Finetti" />