Metaphysical subjectivism

Metaphysical 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.