Deontic Logic

1. Deontic Logic is so mysterious that there isn't even an easy answer to what's it all about. Some would say its subject are the relations between the ordinary language modal operators 'It is obligatory that ...', 'It is forbidden that ...', 'It is permitted that ...', usually formalized as OA, FA, PA, which deontic logic classically treats as analogous to the so-called 'alethic' modalities 'It is necessary that ...', 'It is impossible that ...', 'It is possible that ...'. There is then a dispute on whether the '...' part is to be a factual description like 'the window is closed', an action sentence 'Jörg closes the window', or just anything. Others would more broadly say the subject of deontic logic is the logic of legal or moral discourse (or both), and some like to extend it to the use of imperatives even in scientific discourse ("Let alpha equal zero!").

If you just strolled across this site by means of a search engine, be warned: There are, nowadays, a hundreds of publications on deontic logic. For a good introduction, read Risto Hilpinen's collections "Deontic Logic" (1971) and "New Studies in Deontic Logic" (1981). The best known system of deontic logic is the modal system D, also called 'standard deontic logic' or SDL. But SDL has problems formalizing conditional obligations, and cannot formalize contrary-to-duty obligations (e.g. don't smoke, but if you do at least use an ash-tray). This was the reason why its own authors, Georg Henrik von Wright and Arthur N. Prior, gave up SDL in 1956 in favor of a dyadic approach, that formalizes 'It is obligatory that ... under the condition ...' as O(A/C). Dyadic deontic logic has often been linked to preference reasoning (the best thing, given the situation I am in, or the choice I have, is ...). Dyadic deontic logic has also been linked to non-monotonic logic, since the obligations may change when the circumstances do (e.g. in an example by Plato, a man must return the weapon he borrowed, but not when the lender has become mad or is drunk). One of the strongest dyadic deontic systems is Lennart Åqvist's system G, based on Bengt Hansson's DSDL3. Other people have used settings of temporal logic, of relevant logic or dynamic logic to explain their deontic logic. Even though none of the systems that exist today seems to be free of counterintuitive results (the so-called 'paradoxes of deontic logic'), stopping at SDL would scarcely be state of the art anymore. So please find your way into the literature before you condemn the whole enterprise.

On biannual DEON workshops philosophers, jurists, mathematicians, and computer scientists exchange their views. The next workshop will be held 12-14 July 2006, Utrecht Universität, Netherlands, Europe - visit the DEON 2006 homepage.


(back to fish).

2. I provide some papers of mine below. Tell me what you think of them.







(To view postscript files, get the free programs Ghostscript and Ghostview here. To create postscript files, use a postscript printer driver, change properties to maximize portability, and print to file.)

(back to fish)

3. I am currently combining the questions and results from my DEON 2000 - 2004 and IVR'05 papers into what hopefully will be my doctoral thesis. Though this is of course is my top priority right now, I am also planning more papers, so come back to this page soon.

(Back to fish)

4. If you're interested in online papers on Deontic Logic, consult the page of Leon van der Torre, where some great papers of his can be downloaded. Also try the author-links e.g. on the DEON '98 homepage, some have papers available (back to fish).

5. I had the pleasure of giving a seminar on deontic logic at the Institute for Logic, Leipzig University. For all of you interested, feel free to have a look at my lecture notes, put here as they progress (in German).

(back to fish)