I'm trying to explain to someone that an appeal to consequences is a fallacy in formal logic, but is appropriate when you're discussing policy, for instance, or more generally, when choosing between multiple possible actions. Is there a word for this latter type of argument? I've considered, "rhetoric", "debate", "discourse", and "informal logic", but I'm not sure if any of those are correct.

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    Deontic logic deals with what "should" be the case. You can base a very natural logic of action on such a basis by explicating "x should do y" as "it should be the case that x is brining about y". Commented Sep 20, 2013 at 19:57
  • 1
    This seems to be related to counter-factuals. Commented Sep 21, 2013 at 4:08
  • its the realm of praxis (action) & politics. Commented Sep 21, 2013 at 8:04

3 Answers 3


Deontic logic is concerned with what is optional, recommended, forbidden, etc.

Doxastic logic, on the other hand, is about beliefs.

I would argue that policies (as per the OP) can be expressed by using deontic logic and perhaps doxastic logic as well if you want to capture actual adherence to stated policies. As a practical example, ISO/IEC 24744, a standard language for the description of methodologies, uses deontic markers to express whether specific tasks are compulsory, recommended, optional, discouraged or forbidden.


Normative ethics is the study of prescriptive ethics, what should be done, as opposed to descriptive ethics, which studies ideas of the good.

Normative ethics studies purposive action. It is also referred to as morality.

Here is the Wikipedia

There is also some good rounded out info here: Britanica


Ask: is the consequence good, or bad? This will reveal [a] hidden premise(s). Then you can transform the argument from A implies B to:

  1. B is good.
  2. Doing A results in B.
  3. Therefore A ought to be done.

This might seem correct, but there are still problems looming. For example, let me add a possible hidden premise:

  1. B is good.
  2. C is better than B and mutually exclusive with B.
  3. Doing A results in B.
  4. Therefore A ought to be done.

Here, #4 is clearly false. Another possible hidden premise which would defeat the conclusion is there existing no moral (virtuous) way to get B from A. Of course one could be a Machiavellian, but unless this is a premise, the issue is underspecified and no should is reached.

  • @iphigenie: Are you saying that #3 does not follow? If so, I agree, but my point is that this exposes the fallacy more clearly. To add more, #1 does not say how good B is compared to other things.
    – labreuer
    Commented Oct 7, 2013 at 23:12
  • No. I'm sorry, I should have been more thoughtful. I've read something wrong into your answer. (If you edit it, I will most certainly remove the downvote that is entirely misplaced).
    – iphigenie
    Commented Oct 8, 2013 at 0:23

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