Brian F. Chellas
Professor Emeritus of
1. Why were you initially drawn to formal methods?
I do not know when formal methods first attracted me. My initial awareness of them came in Robert Beard's introductory logic course at Florida State University. But already as a youngster my heart was set on a career as a private detective, and I think my interest in solving mysteries predisposed me to eventual fascination with the logical enterprise.
That is by way of what might be termed a rational account of my beguilement. Years of reflection, and not a little therapy, have persuaded me of an explanation in causal terms. My childhood experience of a broken home and the realization during my teenage years that my mother was an alcoholic engendered a powerful need for order, stability, and predictability. It dominated my thinking until recently, when I left the academy and began playing jazz guitar in earnest. But even in music my enchantment with order and logicality occasionally surfaces. It showed itself early on when, while completing my dissertation, I wrote Chord Systems for the Guitar (1968). And in the past few years I have spent a good deal of time looking for a systematic account of the modes of the alt scale. (When I find it I intend to publish the result as "Modal Logic: An Introduction".)
As a graduate student at Stanford University my interests veered toward philosophy of language and, in particular, Donald Davidson's insight that a Tarski-type theory of truth is a paradigm of a theory of meaning. To better understand this idea I spent a year learning as much logic as I could, and ultimately conjoined logic and philosophy of language in my thesis, The Logical Form of Imperatives (1969), written under the direction of Dana Scott.
Beginning with the dissertation and an offspring article, "Imperatives" (1971), I directed much of my intellectual effort toward questions in deontic logic. I quickly came to see that the deontic logics of the day were fundamentally wrong (my theory of imperatives being a singular exception!), inasmuch as they were construed as normal modal logics and explicated by means of "all possible worlds" interpretations. (In a normal modal logic, necessity is closed under modus ponens and the necessitation of any validity is itself valid.) I was dissatisfied too with concomitant accounts of conditional obligation, especially as these were deployed in the bewitching Paradox of the Good Samaritan. The principal results of my unease are contained in a paper, "The Story of O" (1973), and the article "Conditional Obligation" (1974). The latter was based on a general account of conditionality that appeared in "Basic Conditional Logic", published a year later (1975). These themes are examined as well in my textbook Modal Logic: An Introduction (1980).