Subjectivism
Subjectivism is the doctrine that "our own mental activity is the only unquestionable fact of our experience",[1] instead of shared or communal, and that there is no external or objective truth.
For other uses, see Subjectivism (disambiguation).While Thomas Hobbes was an early proponent of subjectivism,[2][3] the success of this position is historically attributed to Descartes and his methodic doubt. He used it as an epistemological tool to prove the opposite (an objective world of facts independent of one's own knowledge, ergo the "Father of Modern Philosophy" inasmuch as his views underlie a scientific worldview).[1] Subjectivism accords primacy to subjective experience as fundamental of all measure and law.[4] In extreme forms like Solipsism, it may hold that the nature and existence of every object depends solely on someone's subjective awareness of it. One may consider the qualified empiricism of George Berkeley in this context, given his reliance on God as the prime mover of human perception.
In probability[edit]
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".[10] 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.[11] 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.[12][13] In attempting to justify subjective probability, Bruno de Finetti created the notion of 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.[13]