  As a law of probability, this was not new. It was in use since the eighteenth century. It is needed to answer a compulsory question: how likely is it that two events will happen? Answer: it is the probability of the first, multiplied by the probability of the second on the supposition that the first happens. What was novel in Ramsey’s essay was the interpretation of probability as degree of belief; and what was novel in the 1929 paper (1929b) was the linking of “degree of belief in \(q\) given \(p\)” with our ordinary, typically uncertain, conditional judgements.