Subjectivism is the doctrine that "our own mental activity is the only unquestionable fact of our experience", instead of shared or communal, and that there is no external or objective truth. The success of this position is historically attributed to Descartes and his

methodic doubt Cartesian doubt is a form of methodological skepticism associated with the writings and methodology of René Descartes (March 31, 1596Feb 11, 1650). Scruton, R.''Modern Philosophy: An Introduction and Survey''(London: Penguin Books, 1994). Leiber, ...

, although 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). Subjectivism accords primacy to subjective experience as fundamental of all measure and law. In extreme forms like

Solipsism Solipsism (; ) is the philosophical idea that only one's mind is sure to exist. As an epistemological position, solipsism holds that knowledge of anything outside one's own mind is unsure; the external world and other minds cannot be known a ...

, 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.

Metaphysical subjectivism

Subjectivism is a label used to denote the philosophical tenet that "our own mental activity is the only unquestionable fact of our experience."Richardson, Alan and Bowden, John (1983
''A new dictionary of Christian theology''
pp.552-3 The success of this position is historically attributed to Descartes and his

. Subjectivism has historically been condemned by Christian theologians, which oppose to it the objective authority of the church, the Christian dogma, and the revealed truth of the Bible.Dallmayr, Fred Reinhard (1989
''Margins of political discourse''
p.188 Christian theologians, and Karl Barth in particular, have also condemned anthropocentrism as a form of subjectivism. Metaphysical subjectivism is the theory that reality is what we perceive to be real, and that there is no underlying true reality that exists independently of perception. One can also hold that it is

consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...

rather than perception that is reality (

idealism In philosophy, the term idealism identifies and describes metaphysical perspectives which assert that reality is indistinguishable and inseparable from perception and understanding; that reality is a mental construct closely connected t ...

). This is in contrast to

metaphysical objectivism Philosophical realism is usually not treated as a position of its own but as a stance towards other subject matters. Realism about a certain kind of thing (like Mathematical realism, numbers or Moral realism, morality) is the thesis that this kin ...

and

philosophical realism Philosophical realism is usually not treated as a position of its own but as a stance towards other subject matters. Realism about a certain kind of thing (like numbers or morality) is the thesis that this kind of thing has ''mind-independent e ...

, which assert that there is an underlying 'objective' reality which is perceived in different ways. This viewpoint 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 is dependent on that consciousness. This has its philosophical basis in the writings of Descartes (see ''

cogito ergo sum The Latin , usually translated into English as "I think, therefore I am", is the "first principle" of René Descartes's philosophy. He originally published it in French as , in his 1637 ''Discourse on the Method'', so as to reach a wider audien ...

''), and forms a cornerstone of Søren Kierkegaard's philosophy.

Modern versions

Recently, more modest versions of metaphysical subjectivism have been explored. For example, I might hold that it is a ''fact'' that chocolate is tasty, even though I recognize that it is not tasty to everyone. This would imply that there are facts that are ''subjective''. (Analogously, one might hold that it is a fact that it is winter in the Northern Hemisphere, even though this is not always the case, implying that some facts are ''temporary''.) Giovanni Merlo has developed a specific version of metaphysical subjectivism, under which subjective facts always concern ''mental'' properties. With Giulia Pravato, he has argued that his version of subjectivism provides a natural way to be both a realist and a

relativist Relativism is a family of philosophical views which deny claims to objectivity within a particular domain and assert that valuations in that domain are relative to the perspective of an observer or the context in which they are assessed. Ther ...

about, for example, the proposition that chocolate is tasty -- it is part of reality (a subjective fact) that chocolate is tasty, but that doesn't mean it's necessarily true from another's point of view. Caspar Hare's theory of

egocentric presentism Egocentric presentism is a form of solipsism introduced by Caspar Hare in which other persons can be conscious, but their experiences are simply not . Similarly, in related work, Hare argues for a theory of perspectival realism in which other pers ...

is another, closely related example.

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 In metaphilosophy and ethics, meta-ethics is the study of the nature, scope, and meaning of moral judgment. It is one of the three branches of ethics generally studied by philosophers, the others being normative ethics (questions of how one ought ...

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). Consider the case this way — to a person imagining what it's like to be a cat, catching and eating mice is perfectly natural and morally sound. To a person imagining they are a mouse, being hunted by cats is morally abhorrent. Though this is a loose metaphor, it serves to illustrate the view that each individual subject has their own understanding of right and wrong. 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 depending on situation.

In probability

Broadly speaking, there are two views on

Bayesian probability Bayesian probability is an interpretation of the concept of probability, in which, instead of frequency or propensity of some phenomenon, probability is interpreted as reasonable expectation representing a state of knowledge or as quantification ...

that interpret the probability concept in different ways. In

probability Probability is the branch of mathematics concerning numerical descriptions of how likely an event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and 1, where, roughly speakin ...

, 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". 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. According to the objectivist view, the rules of

Bayesian statistics Bayesian statistics is a theory in the field of statistics based on the Bayesian interpretation of probability where probability expresses a ''degree of belief'' in an event. The degree of belief may be based on prior knowledge about the event, ...

can be justified by requirements of rationality and consistency and interpreted as an extension of logic. 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. de Finetti, B. 1974. ''Theory of Probability'' (2 vols.), J. Wiley & Sons, Inc., New York). In attempting to justify subjective probability,

Bruno de Finetti Bruno de Finetti (13 June 1906 – 20 July 1985) was an Italian probabilist statistician and actuary, noted for the "operational subjective" conception of probability. The classic exposition of his distinctive theory is the 1937 "La prévision: ...

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 A thought experiment is a hypothetical situation in which a hypothesis, theory, or principle is laid out for the purpose of thinking through its consequences. History The ancient Greek ''deiknymi'' (), or thought experiment, "was the most anc ...

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.

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