Peter K. Schotch

Some Remarks on (Weakly) Weak Modal Logics

R. E. JENNINGS and P. K. SCHOTCH*The weakest modal logics have not come in for much attention fromlogicians or philosophers principally, it seems, because they are supposedlyincapable of supporting interpretations of much philosophical succulence.But from the point of view of general semantic theory they deserve moreattention than they get, for it is only by a study of weak modal logics thatwe come to appreciate many of the limitations of the now standard seman-tical methods. A multitude of examples bears this out. In the theory of first-order definability in modal logic valuable insights would have been lost hadwe restricted our attention to extensions of S4. The McKinsey formula M

On preserving : essays on preservationism and paraconsistent logic

Paraconsistent logic is a theory of reasoning in philosophy that studies inconsistent data. The discipline has several different schools of thought, including preservationism, which responds to the problems that arise when human beings continue to reason when faced with inconsistent data. On Preserving is the first complete account of the Preservationist School, which developed in Canada out of the early work of Raymond Jennings, Peter Schotch, and their students. Assembling the previously scattered works of the Preservationist School, this collection contains all of the most significant works on the basic theory of the preservationist approach to paraconsistent logic. With essays both written and rewritten specifically for this volume, the contributors cover topics that include the motivation for the preservationist approach, as well as more technical results of their research. Concise and unified, On Preserving is the ideal introduction to a distinct philosophical field.

Logic and aggregation

Paraconsistent logic is an area of philosophical logic that has yet to find acceptance from a wider audience. The area remains, in a word, disreputable. In this essay, we try to reassure potential consumers that it is not necessary to become a radical in order to use paraconsistent logic. According to the radicals, the problem is the absurd classical account of contradiction: Classically inconsistent sets explode only because bourgeois classical semantics holds, in the face of overwhelming evidence to the contrary, that both A and ∼ A cannot simultaneously be true! We suggest (more modestly) that there is, at least sometimes, something else worth preserving, even in an inconsistent, unsatisfiable premise set. In this paper we present, in a new guise, a very general version of this “preservationist” approach to paraconsistency.

Remarks on the Scott---Lindenbaum Theorem

In the late 1960s and early 1970s, Dana Scott introduced a kind of generalization (or perhaps simplification would be a better description) of the notion of inference, familiar from Gentzen, in which one may consider multiple conclusions rather than single formulas. Scott used this idea to good effect in a number of projects including the axiomatization of many-valued logics (of various kinds) and a reconsideration of the motivation of C.I. Lewis. Since he left the subject it has been vigorously prosecuted by a number of authors under the heading of abstract entailment relations where it has found an important role in both algebra and theoretical computer science. In this essay we go back to the beginnings, as presented by Scott, in order to make some comments about Scott’s cut rule, and show how much of Scott’s main result may be applied to the case of single-conclusion logic.

Worlds and times

In the fourteenth century, Duns Scotus suggested that the proper analysis of modality required not just moments of time but also “moments of nature”. In making this suggestion, he broke with an influential view first presented by Diodorus in the early Hellenistic period, and might even be said to have been the inventor of “possible worlds”. In this essay we take Scotus’ suggestion seriously devising first a double-index logic and then introducing the temporal order. Finally, using the temporal order, we define a modal order. This allows us to present modal logic without the usual interpretive questions arising concerning the relation called variously ‘accessibility’, ‘alternativeness’, and, ‘relative possibility.’ The system in which this analysis is done is one of those which have come to be called a hybrid logic.