Metaphysical subjectivismMetaphysical subjectivism is the theory that perception creates 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 creates reality. This is in contrast to metaphysical objectivism. The invention of machines that can "see", "hear", or otherwise observe and record events provides a thought experiment (offered by Winston Churchill, who is not otherwise known as a philospher) that is difficult for subjectivists to explain. Let us set up automatic camera to record events in a place that no human (or other creature reasonably considered "conscious") can observe. Say that it is set inside a volcano, for example. The camera is later retrieved and its photographs, with date markings, are observed. Did the events recorded in the photographs really happen even though no one consciously observed them? Did the conscious observation of the photographs themselves somehow suddenly cause them to depict events that apparently happened at an earlier time? 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, and that physical objects do exist. They conceive, however, that the nature of reality as related to a given consciousness unit is created and governed by that consciousness. Subjectivism in probability In probability, a aubjectivist would tell you that probabilities are simply degree-of-beliefs by rational agents, with no objective reality. Unlike a frequentist, a subjectivist would be happy to accept that we can deduce the probability that the sun will rise again tomorrow merely from its age, colour, chemical composition, and so forth. Unlike an objectivist, a subjectivist has no problem with differing people giving different probabilities to something happening, and all being correct. In practice, it's quite tricky to get humans (or, if we ever met any, other rational agents) to tell you what their degrees of belief are - we do all kinds of things like hedging our bets, peer pressure, being suspeicious, trusting our friends, or looking for patterns - in general, all the things which mark us as intelligent beings but probability researchers seem to see as a downside. To get round this, people normally call upon people to 'put their money where their probabilities are'. Specifically, when someone states their degree-of-belief in something other experimental subjects are free to place small bets (usually with plastic tokens) for or against that belief, with appropriate odds. Confronted with material gain or loss, most people quickly change their quoted odds to be more accurate. So effective is this method that it's been designated by some as the fundamental meaning of probability: the willingness to take or place a bet.