 On this traditional approach, we are invited to think of justification as measured by how probable the belief is given the reasons or evidence you have. One convenient way to measure probability is to use the decimals in the interval [0, 1]. A probability of 0 means that the claim is guaranteed to be false. A probability of 1 means that the claim is guaranteed to be true. A probability of .5 means that the claim is just as likely to be true as it is to be false. The question then becomes, how probable must your belief be for it to be knowledge?