We must stay where we are. You would not think it, to look at them. There is no a priori probability about it. He remarks that, while the individual man is an insoluble puzzle, in the aggregate he becomes a mathematical certainty. You can, for example, never foretell what any one man will do, but you can say with precision what an average number will be up to.
Individuals vary, but percentages remain constant.
So says the statistician. From all this, we can conclude that Sherlock Holmes knew well the new probabilistic theory of scientific reasoning, and applied it, as his own method, to his criminal investigations. Moreover, since the major advocates of this new theory were also an expert of symbolic logic, we may conclude, in all probability, that Holmes knew Boolean symbolic logic as well. On the total evidence, the balance of probability is that he was a very good logician. Bibliography De Morgan, Augustus.