The subject of this book is the reasoning under uncertainty based on
sta- tistical evidence, where the word reasoning is taken to mean
searching for arguments in favor or against particular hypotheses of
interest. The kind of reasoning we are using is composed of two aspects.
The first one is inspired from classical reasoning in formal logic,
where deductions are made from a knowledge base of observed facts and
formulas representing the domain spe- cific knowledge. In this book, the
facts are the statistical observations and the general knowledge is
represented by an instance of a special kind of sta- tistical models
called functional models. The second aspect deals with the uncertainty
under which the formal reasoning takes place. For this aspect, the
theory of hints [27] is the appropriate tool. Basically, we assume
that some uncertain perturbation takes a specific value and then
logically eval- uate the consequences of this assumption. The original
uncertainty about the perturbation is then transferred to the
consequences of the assumption. This kind of reasoning is called
assumption-based reasoning. Before going into more details about the
content of this book, it might be interesting to look briefly at the
roots and origins of assumption-based reasoning in the statistical
context. In 1930, R. A. Fisher [17] defined the notion of fiducial
distribution as the result of a new form of argument, as opposed to the
result of the older Bayesian argument.