Quantum Mechanics assigns a probability of measuring a final state given an initial state. This suggests a conditional probability of obtaining |final> on the condition that you first have |initial>. But since the probability of |s> obtained from the same initial state |s> is 1, in other words <s|s>=1, it would seem that the conditional probability would be normalized by dividing by the probability of obtaining |initial> to begin with. I thought I read at one point how QM might be understood in terms of conditional probabilites, and I wonder if anyone can point me to some reference somewhere. Thanks.