Sampling scholarly arguments: a test of a theory of good inference

For some years, I have been developing a general theory of inference appraisal (Hitchcock 1985, 1992, 1994, 1998). According to a current version of this theory, a conclusion follows (conclusively, provisionally, etc.) from premisses adduced in its support if and only if some covering generalization of the argument is non-trivially acceptable (always, provisionally, etc.). By a covering generalization is meant a generalization of the conditional sentence whose antecedent is the conjunction of the premisses and whose consequent is the conclusion. Such a generalization is acceptable if and only if it deserves to be accepted by the appraiser; criteria of acceptability may vary between appraisers and between different types of sentences (empirical, normative, evaluative, etc.). The acceptability of a generalized conditional is non-trivial if it is based neither on the (universal, provisional, etc.) unacceptability of its antecedent nor on the (universal, provisional, etc.) acceptability of its consequent. This admittedly schematic theory gives us what we want out of a good inference: transmission of acceptability from premisses to conclusion. It covers conclusive as well as nonconclusive inferences. It captures the generality of inference claims which is implicit in the human practice of refutation by logical analogy. It covers speech acts for which truth seems an inapplicable criterion of acceptability–such as recommendations, evaluations and requests. It provides a touchstone for testing proposed reasoning schemes or argument schemes expressed at a lower level of generality. And it fits our practices of reasoning and argument much better than the widely accepted view that good inference is a matter of formal deductive validity or conformity to canons of a formal inductive logic. For example, looking at the grey sky and blowing tree branches outside my window, I may infer that today’s forecast of rain is likely to be correct. If I were to verbalize this inference, I would do so somewhat as follows: “It probably will rain today: the sky is a leaden grey, and the tree branches outside my window are blowing furiously in the wind.” I would not include an extra premiss which would make my reasoning formally valid, such as: “Whenever the sky is a leaden grey, and the tree branches outside my window are blowing furiously in the wind, it is going to rain.” This covering generalization is non-trivially true for the most part, as we know by experience and elementary meteorology. Its acceptability means that, according to the theory sketched above, the conclusion of my inference follows from the premisses just as they are stated, without supplementation. One way to test any such theory is to apply it to actual reasonings. For this purpose, it is desirable to have a sample which is likely to be representative of the variety of ways in which human beings draw conclusions. I used random methods to extract a sample of 50 inferences from several hundred thousand English-language books catalogued in the library of a researchintensive university. In this paper I describe the method of sampling, the criteria for identifying inferences, and the results of applying the above theory to the 50 inferences.