Talk:Deontic logic

message: Nice job, User:Dbtfz! But I guess you shouldn't have deleted all the information from the previous version. For instance, the reference to Jørgensen's Dilemma and to norms. And it is not clear whether one should say that DL is a branch of modal logic, since there were (von Wright's) and there are DL systems come right from first-order predicate logic. There are also some minor spelling mistakes and the like that I'll fix as soon as I'm sober. Velho 04:25, 29 January 2006 (UTC)
replies: text: I agree with your points, and encourage you to expand and edit the article accordingly.  Best, Dbtfz (talk - contribs) 16:17, 29 January 2006 (UTC)
replies: text: Thanks for the reply and the last edit! I'll do a tiny copy-edit within the next hours. Don't know if I mentioned it, but you did a very good job! Velho 18:24, 29 January 2006 (UTC)
thread_title: Untitled

message: The "paradoxes" claimed by the article are totally unsatisfactory.  Unless valid proofs that they are paradoxical can be provided, they are not worth mentioning.  Ross is clearly incorrect by reductio ad absurdum.  ‣ᓛᖁ[ ᑐ] 19:19, 10 February 2006 (UTC)
replies: text: What's the point?  I take it you are not disputing that they are theorems, but that the theorems are counterintuitive? --- Charles Stewart(talk) 19:54, 10 February 2006 (UTC)
replies: text:  None of these are paradoxes; they can all be reduced to something self-consistent.  Ross's theorem doesn't seem to follow logically from D: OA \rightarrow (OA \lor OB) seems to be an intended intermediate step, but why should O be distributive over \lor?  He's also neglected the fact that B \rightarrow \lnot PA.  ‣ᓛᖁ[ ᑐ] 20:59, 10 February 2006 (UTC)
replies: text:  It is indeed arguable whether the so-called "paradoxes of deontic logic" are really paradoxes.  (Personally, I think it is reasonable to classify them as such, but I don't have time to argue for this at the moment.)  Many writers on the topic of these "paradoxes" qualify their discussion with a remark to the effect that the problems in question are not really "paradoxes," strictly speaking.  However, the term "paradoxes of deontic logic" is very widely used in the literature; and given that the point of this article is to document existing knowledge on, and theories about, the topic, it seems appropriate to stick with the standard terminology.  A comment regarding the dubious application of the term "paradox" would very much be in order, though.  Also, it would of course be very appropriate to discuss possible resolutions--especially those that have been proposed in the literature.  Obviously, this is not the venue for original research on the topic.  Dbtfz (talk - contribs) 21:51, 10 February 2006 (UTC)
replies: text:  Maybe the sections should just be called something other than paradoxes?JoelSCollier 14:20, 15 December 2006 (UTC)
thread_title:  False paradox 

message: Standard deontic logic has several features that are found by some to be counterintuitive.  These are sometimes referred to as the "paradoxes of deontic logic."
=== Ross's paradox ===
The following is a theorem of D:
: OA \rightarrow O(A \lor B)
Thus if I ought to mail the letter, I ought to mail the letter or burn it!  This is called Ross's paradox after the Danish philosopher Alf Ross.
=== Prior's paradox ===
The following is a theorem of D:
:FA \rightarrow O(A \rightarrow B)
Thus if it is forbidden to jaywalk,  it ought to be that if I jaywalk I am given the death penalty.  This is called Prior's paradox after A. N. Prior.
=== The Good Samaritan paradox ===
Consider the following statements:
* It ought to be that Alice refrains from robbing Bob.
* It ought to be that Claire (the Good Samaritan) helps Bob, whom Alice has robbed.
These statements, when expressed in ordinary language, seem perfectly consistent (i.e. they could both be true at the same time).  However, when formalized in D, they entail that Claire both ought and ought not to help Bob.  This paradox was first noted by the Swedish philosopher Lennart Åqvist.
=== Chisholm's paradox ===
Consider the following statements:
* Alice ought to go to the assistance of her neighbors.
* It ought to be that if she does go, she tell them she is coming.
* If she does not go, she ought not to tell them she is coming.
* She does not go.
When formalized in D, these entail that Alice both ought and ought not to go the assistance of her neighbors.  This is called Chisolm's paradox after the philosopher Roderick Chisholm.
There has been a great deal of discussion of these and related "paradoxes."  Some believe that the paradoxes can be explained away, while others believe that they jointly constitute a reductio ad absurdum of standard deontic logic.
:I think this is only paradoxical if you forget what a conditional is. Two plus two is necessarily four, so it ought to be four. Given that Alice does not go, she ought not to go (since A implies A is a necessary truth, it ought to be true). But she ought to go. Therefore she ought to go and ought not to go. This is obviously true and not in the least paradoxical.
:Ross's paradox and the Good Samaritan are likewise obvious truths. (Ross's is so obvious that I find it strange anyone could consider it paradoxical!) Prior's paradox is an obvious truth if you remember that A->B means "either not-A or B". If it's obligatory that I not jaywalk, then it's obligatory that it be the case that either I not jaywalk or I get the death penalty. 91.107.151.20 (talk) 00:27, 24 December 2008 (UTC)
replies: text: If it's obligatory that it be the case that either I not jaywalk or I get the death penalty, then it's obligatory that if I jaywalk, I get the death penalty. I don't quite understand how this analysis gets rid of the problem... Do you mean that these aren't strictly paradoxes? But they're true premises that yield false conclusions! Which shows that something seriously wrong has happened along the way. i.e., the rules of logic were faulty.--Heyitspeter (talk) 09:36, 16 March 2009 (UTC)
replies: text: Er... maybe I don't understand what you mean... "Therefore she ought to go and ought not to go. This is obviously true and not in the least paradoxical." In D, this allows you to derive P and not-P. That's a contradiction. Is it that you don't think a contradiction is paradoxical?--Heyitspeter (talk) 09:46, 16 March 2009 (UTC)

text: Hi, I am doing my PhD on this topic, it is really absurd to leave these paradoxes out (and yes, pretty much every paper prepends paradox with the caveat "so-called"). Additionally, this article should have contrary-to-duty norms, where Mally went wrong (there is a paper from 2004 on this) and tie it in with normative frameworks. It may also be extended to include topics such as sanctions, reparation of violations, temporal aspects, normative conflict and normative system change (the latter problem which has been formalized using a variant of the AGM belief revision postulates). Having said that, I don't have time to do this, as I'm actually trying to do my own research. But a personal thank you who anyone who does.  Academic Pretzel (talk) 09:18, 12 July 2013 (UTC)
thread_title:  The paradoxes of deontic logic 

message: Consider the following statements:
* Alice ought to go to the assistance of her neighbors.
* It ought to be that if she does go, she tell them she is coming.
* If she does not go, she ought not to tell them she is coming.
* She does not go.
When formalized in D, these entail that Alice both ought and ought not to go the assistance of her neighbors.  This is called Chisolm's paradox after the philosopher Roderick Chisholm.
There has been a great deal of discussion of these and related "paradoxes."  Some believe that the paradoxes can be explained away, while others believe that they jointly constitute a reductio ad absurdum of standard deontic logic.
:I think this is only paradoxical if you forget what a conditional is. Two plus two is necessarily four, so it ought to be four. Given that Alice does not go, she ought not to go (since A implies A is a necessary truth, it ought to be true). But she ought to go. Therefore she ought to go and ought not to go. This is obviously true and not in the least paradoxical.
:Ross's paradox and the Good Samaritan are likewise obvious truths. (Ross's is so obvious that I find it strange anyone could consider it paradoxical!) Prior's paradox is an obvious truth if you remember that A->B means "either not-A or B". If it's obligatory that I not jaywalk, then it's obligatory that it be the case that either I not jaywalk or I get the death penalty. 91.107.151.20 (talk) 00:27, 24 December 2008 (UTC)
replies: text: If it's obligatory that it be the case that either I not jaywalk or I get the death penalty, then it's obligatory that if I jaywalk, I get the death penalty. I don't quite understand how this analysis gets rid of the problem... Do you mean that these aren't strictly paradoxes? But they're true premises that yield false conclusions! Which shows that something seriously wrong has happened along the way. i.e., the rules of logic were faulty.--Heyitspeter (talk) 09:36, 16 March 2009 (UTC)
replies: text: Er... maybe I don't understand what you mean... "Therefore she ought to go and ought not to go. This is obviously true and not in the least paradoxical." In D, this allows you to derive P and not-P. That's a contradiction. Is it that you don't think a contradiction is paradoxical?--Heyitspeter (talk) 09:46, 16 March 2009 (UTC)

text: Hi, I am doing my PhD on this topic, it is really absurd to leave these paradoxes out (and yes, pretty much every paper prepends paradox with the caveat "so-called"). Additionally, this article should have contrary-to-duty norms, where Mally went wrong (there is a paper from 2004 on this) and tie it in with normative frameworks. It may also be extended to include topics such as sanctions, reparation of violations, temporal aspects, normative conflict and normative system change (the latter problem which has been formalized using a variant of the AGM belief revision postulates). Having said that, I don't have time to do this, as I'm actually trying to do my own research. But a personal thank you who anyone who does.  Academic Pretzel (talk) 09:18, 12 July 2013 (UTC)
thread_title:  Chisholm's paradox