  Now, suppose we have an initial situation in which Colour(A, Red) and Position(A, House) hold. According to the machinery of deductive logic, what then holds after the action Paint(A, Blue) followed by the action Move(A, Garden)?  Intuitively, we would expect Colour(A, Blue) and Position(A, Garden) to hold. Unfortunately, this is not the case. If written out more formally in classical predicate logic, using a suitable formalism for representing time and action such as the situation calculus (McCarthy &amp; Hayes 1969), the two formulae above only license the conclusion that Position(A, Garden) holds.  This is because they don't rule out the possibility that the colour of A gets changed by the Move action.