Subjectivism

Subjectivism is a philosophical tenet that accords primacy to subjective experience as fundamental of all measure and law. In an extreme form, it may hold that the nature and existence of every object depends solely on someone's subjective awareness of it. For example, Wittgenstein wrote in Tractatus Logico-Philosophicus: "The subject doesn't belong to the world, but it is a limit of the world" (proposition 5.632). One may also consider the qualified empiricism of George Berkeley in this context, given his reliance on God as the prime mover of human perception.

Metaphysical subjectivism
Metaphysical subjectivism is the theory that perception is reality, and that there is no underlying, true reality that exists independent of perception. One can also hold that it is consciousness rather than perception that is reality. This is in contrast to metaphysical objectivism, which asserts that there is an underlying 'objective' reality which is perceived in different ways.

This holding should not be confused with the stance that "all is illusion" or that "there is no such thing as reality." Metaphysical subjectivists hold that reality is real enough. They conceive, however, that the nature of reality as related to a given consciousness unit is dependent on that consciousness. This has its philosophical basis in the writings of Descartes (see Cogito Ergo Sum),

Subjectivism and panpsychism
One possible extension of subjectivist thought is that conscious experience is available to all objectively perceivable substrates. Upon viewing images produced by a camera on the rocking side of an erupting volcano, one might suppose that their relative motion followed from a subjective conscious within the volcano. These properties might also be attributed to the camera or its various components as well.

In this way, though, subjectivism morphs into a related doctrine, panpsychism, the belief that every objective entity (or event) has an inward or subjective aspect.

Ethical subjectivism
Ethical subjectivism is the meta-ethical belief that ethical sentences reduce to factual statements about the attitudes and/or conventions of individual people, or that any ethical sentence implies an attitude held by someone. As such, it is a form of moral relativism in which the truth of moral claims is relative to the attitudes of individuals (as opposed to, for instance, communities).

An ethical subjectivist might propose, for example, that what it means for something to be morally right is just for it to be approved of. (This can lead to the belief that different things are right according to each idiosyncratic moral outlook.) One implication of these beliefs is that, unlike the moral skeptic or the non-cognitivist, the subjectivist thinks that ethical sentences, while subjective, are nonetheless the kind of thing that can be true or false.

Subjectivism in probability
In probability, a subjectivism stands for 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. 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. See Bayesianism.

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.