ABSTRACT
We infer some claims on the basis of other claims: we move from premises to a conclusion. Some inferences are deductive: it is impossible for the premises to be true but the conclusion false. All other inferences I call ‘inductive’, using that term in the broad sense of non-demonstrative reasons. Inductive inference is thus a matter of weighing evidence and judging probability, not of proof. How do we go about making these judgments, and why should we believe they are reliable? Both the question of description and the question of justification arise from underdetermination. To say that an outcome is underdetermined is to say that some information about initial conditions and rules or principles does not guarantee a unique solution. The information that Tom spent five dollars on apples and oranges and that apples are fifty cents a pound and oranges a dollar a pound underdetermines how much fruit Tom bought, given only the rules of deduction. Similarly, those rules and a finite number of points on a curve underdetermine the curve, since there are many curves that would pass through those points.
