Strictly speaking, the only question that can be asked in physics is: What fraction of states satisfying condition A also satisfy condition B? The answer to this is a number between 0 and 1, which can be interpreted as a conditional probability, written as P(B | A). In terms of path integration, since P(B | A) = ⁠ P(A ∩ B) / P(A) ⁠, this means