This article is about the metaphysical and epistemological theory. For other theories known under the same term, see objectivism.

Metaphysical objectivism is the theory that there is an underlying reality that exists independent of our perception and consciousness. This is in contrast to metaphysical subjectivism.

The famous riddle "If a tree falls in the forest, but no one is present to hear it, does it make a sound?" illustrates the difference between the two positions. A metaphysical objectivist would say the answer is yes--the tree does make a sound when no one is around to hear it. The metaphysical subjectivist would say it doesn't. Theological positions complicate the question--for example, George Berkeley would argue that the tree always makes a sound because God is always present to hear it.

Objectivism in probability

In probability, objectivism is the belief that probabilities are real: they're not just numbers we make up or guess, but have a real significance. For example, suppose you flip a coin without looking at it, and then cover it with a piece of paper. Many would say that although there is a 50% chance that it is either heads or tails, nevertheless the coin is actually either one or the other. An objectivist would instead say that the coin itself has a probability of 50% of being heads or tails, regardless of whether anyone is thinking about the subject.

Objectivism comes unstuck when two people have differing probability estimates for the same thing. For example, suppose you are at a party where the host has scribbled either a zero or a one on everyone's forehead, and there are no mirrors. Now consider the question of what the probability is that your forehead reads zero - an objectivist would say that it is either probability one or zero, which the other guests know - but that you have to estimate it to be a half. This can feel somewhat unwieldy and unnatural.

One curious formula for the probability that the sun would rise was given by Laplace, an objectivist. He claimed that this probability was

where d is the number of days that the sun has risen - and that this formula applied in all cases where we knew nothing (or where what we did know was swamped by what we didn't); see also Rule of succession.