CHAPTER 1
PLAUSIBLE REASONING
\The actual science of logic is conversant at present only with things either certain,impossible, or entirely doubtful, none of which (fortunately) we have to reason on.Therefore the true logic for this world is the calculus of Probabilities, which takes account of the magnitude of the probability which is, or ought to be, in a reasonable man's mind." | James Clerk Maxwell (1850)
Suppose some dark night a policeman walks down a street, apparently deserted; but suddenly he hears a burglar alarm, looks across the street, and sees a jewelry store with a broken window. Then a gentleman wearing a mask comes crawling out through the broken window, carrying a bag which turns out to be full of expensive jewelry. The policeman doesn't hesitate at all in deciding that this gentleman is dishonest. But by what reasoning process does he arrive at this conclusion? Let us rst take a leisurely look at the general nature of such problems.