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

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 (d+1)/(d+2), 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). It's not entirely clear where he pulled this figure from, but it does seem to work.