ABSTRACT
However (a) and (b) are not equivalent. Suppose that A and B are friends. The probability that B is in hospital, given that A sends B flowers, is higher than the probability that B is in hospital, given that A does not send B flowers. Nevertheless, A’s sending B flowers is a sign of B’s having gone to hospital, not the source of that move. A does not raise the probability of B being in hospital – not, in the intended, practical sense of that phrase – by sending B flowers and there is no question of A’s exercising power over B.
