Some Slides on Topics from Previous Classes

Table of Contents

Some more problems in Von Wright


If an act and its negation are both permitted, the act is called (morally) indifferent.


Missing fine-grained distinctions. Optionality vs. Indifference.

Commitments / Conditional Norms


See criticism by Chisholm.

Modelling Chisholm: the logical challenge

see other slides.

Deontic vs. Factual Detachment Principles

Factual Detachment
  1. \(a\) and
  2. \(a\) commits you to \(b\).

Then \(Ob\).

Deontic Detachment
  1. \(Oa\) and
  2. \(a\) commits you to \(b\)

then \(Ob\).

Generalised Deontic Detachment
  1. \(a\) commits you to \(b\), and
  2. \(b\) commits you to \(c\).

then \(a\) commits you to \(c\).

Difference: Specificity vs. CTDs

Overshadowing vs. Cancelling. (Torre/Tan)


Entered on [2015-05-21 Thu 07:47]

  • strong (Forrester) vs. weak (no conflict btw. specific obligation and general one)



  • You ought not to tell Reagan nor Gorbatjov.
  • If you tell Reagan you ought to tell Gorbatjov.
  • If you tell Gorbatjov you ought to tell Reagan.
  • You ought not to have a reason to apologise (e.g., to your neighbor, etc.).
  • If you have no reason to apologise you ought not to apologise.
  • If you have a reason to apologise, you should apologise.
Prakken, white fence etc
rules of a game
  • Every player ought to pay X every round.
  • If some player forgot to pay X some round, the next round the other player ought not to pay either.
  • If you get the OK from the tower, you ought to not wait for another signal and take off at 10pm.
  • If you get the OK from the tower but you don't take off at 10pm, you ought to wait for another signal.
  • You ought not to use your mobile phone during the course.
  • However, if you do, use it in order to enlarge your understanding of things taught in the course.
uni-life 2: your parents may tell you:
  • You should be present at your course.
  • If you're not, then you should at least study in the library.
  • You ought not to cheat.
  • However, if you cheat, don't get caught cheating.
  • You ought not to steal.
  • If you steal, steal from the rich.


authorisations (Chisholm style)
  • You ought to do your homework.
  • If you do your homework you are permitted to hang out with your friends.
  • If you do not do your homework, you ought to not hang out with your friends.

A look back at Prior's Paradox (the good Samaritan)

You ought to help you neighbor who has been robbed.

  • adverbial who has been robbed

Problem: helping the neighbor who has been robbed implies that the neighbor has been robbed.

Inheritance principle
If a entails b then Oa entails Ob.
(no term)
Intuitive but leads to absurdity: The neighbor ought to be robbed.

Forrester's response

It's just a scope-problem:

  • Help neighbor: h
  • Neighbor has been robbed: r
  • Phrase it like: \(O(h) \wedge r\) instead of \(O(h \wedge r)\)
  • Problem: does it really represent the informal phrasing?

Additional worries

  • Help(Smith who has been robbed) is logically equivalent to Help(Smith) and Smith has been robbed.
  • If a and b are logically equivalent then Oa and Ob are as well.
  • But then: Ought(Help(Smith who has been robbed)) is equivalent to Ought(Help(Smith) and Smith has been robbed).
  • If we think there is nothing wrong with the first formulation we have to accept the second one. With the Inheritance principle we run into the old problems.

What about a conditional equivalence principle?

What do you think about:

Conditional Equivalence principles
  1. If \(a\) then \(Ob\).
  2. \(a \vdash b \equiv c\)

Then: If \(a\) then \(Oc\).

Think about it and evaluate it as a principle for

  • action types
  • state of affairs.


Action types:

  • You should not kill.
  • If you kill, inflict as little pain as possible.
  • If you kill, inflicting as little pain as possible is equivalent to killing gently.
  • Hence, if you kill, kill gently.

More trouble with inheritance

Question: \(O(a_1 \wedge \ldots \wedge a_n)\) implies \(O(a_i)\)?

  • birthday cake example
  • knowers paradox

Sing and Dance!

Question: does the following principle hold (Cautious Transitivity)

  • If
    1. \(a\) commits you to \(b\)
    2. \(a\) and \(b\) commits you to \(c\)
  • then \(a\) commits you to \(c\)?

Parent and Van der Torre argue: NOPE!


  • If
    1. \(a\) commits you to \(b\)
    2. \(a\) and \(b\) commits you to \(c\)
  • then \(a\) commits you to \(b \wedge c\)?

This shows again, that there are cases which violate inheritance.

How to distinguish cases in which inheritance holds?

What about:

Independence Inheritance Principle
  1. \(O(a \wedge b)\) and
  2. If \(\neg b\) you ought to \(a\).

then \(Oa\).