The title of this dissertation, Modalities in Medieval Logic, combines two temporally distinct and seemingly disparate fields of logic. The use of term ‘modalities’ in the plural, as opposed to ‘modality’ in the singular, is one of the hall-marks of recent developments in logic, which recognizes that there is no single ‘correct’ choice of modality, but that rather a range of modalities can be fruitfully studied with the tools of formal modal logic. This modern view can be contrasted with the distinctly non-modern view of logic indicated by the other part of the title, ‘medieval’, which brings to mind the narrow and rigid formal system of syllogistics
This apparent discrepancy between the two parts of the title immediately raises the question of what can possibly be gained from combining modern logic and medieval logic in the same research programme. Another way to state this question is to split it into two, and to ask what benefit a modern logician might have from looking at medieval logic, and what benefit a historian of medieval logic might have from looking at modern logic.
At a very general level, there are two reasons why the study of medieval logic is of interest to the modern logician. The first reason is to see how closely medieval logical theories in different branches (modal logic, temporal logic, quantifier logic, etc.) resemble modern logical theories in these same branches. The second is tosee how much they differ. If the medieval theory is similar to the modern theory, one can ask to what extent we can shed new light on the medieval theory by modeling it with modern formal tools. If the medieval theory differs from the modern theory, one can ask what the causes of these differences are, whether they
are purely historical, accidental, or whether they reflect conscious differences in
goals and aims, and, if the latter, what we can learn from these differences.
On the other side of the question, a similar answer can be given. Many medieval logical theories often leave something to be desired in terms of clarity. This can be the result of at least two different factors. The first is that the medieval theories were developed within natural language, and even when this Chapter 1. The changing scope of logic natural language is used in a semi-formal fashion, the possibility for ambiguity still remains. The second is that because medieval logical theories were developed essentially as tools for modeling specific philosophical and theological problems, they often carry extra, non-logical, baggage. Abstracting away from this baggage, often metaphysical in nature, allows for a clearer understanding of the underlyinglogical theory.