The approach adopted, at least at the beginning of this book, is based firmly on reason, the wonderful facility that human beings possess, enabling them to comprehend and manipulate the world about them; and only later will emotional and spiritual aspects of uncertainty be considered. “Reason centers attention on the faculty for order, sense, and rationality in thought” says Webster's dictionary, going on to note that “reason is logic; its principle is consistency: it requires that conclusions shall contain nothing not already given in their premises”. A contrasting concept is emotion “the argument which is not an argument, but an appeal to the emotions”.
The program that will be adopted is to state some properties of uncertainty that seem simple and obvious, the premises mentioned in the second quotation above, and from them to deduce by reasoning other, more complicated properties that can be usefully applied. As an example of a premise, suppose you think it is more likely to rain tomorrow than that your train today will be late; also that the latter event is more likely than that your car will break down on traveling to the railway station; then it is necessary that you think rain is more likely than the breakdown. The references to rain, trains, and accidents are not important; the essential concept is contained in an abstraction. Recalling our use of “you”, “event”, and “belief” as described in § 1.7, the premise is that if you have ...