Practice question · Multiple choice
Why must deontic logic reject the principle that whatever is necessary is actually true?
Hints
- Read the box as "it is obligatory that".
- The principle would then say that everything obligatory actually happens.
Show the answer
D. Obligations are frequently unmet, so "ought" must not imply "is"
Why
Under the deontic reading the principle says every obligation is met, which is plainly false, and a logic asserting it could not represent wrongdoing at all. The principle is valid where accessibility is reflexive; deontic accessibility is not.
Practise Modal Logic: Necessity and Possibility
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More questions on Modal Logic: Necessity and Possibility
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