Full Idea
Prescriptivism holds that if you think one 'ought' to do a certain kind of act, and yet you are not committed to doing that act in the relevant circumstances, then you either spoke insincerely, or are using the word 'ought' in a weak sense.
Gist of Idea
Prescriptivism says 'ought' without commitment to act is insincere, or weakly used
Source
Brad W. Hooker (Prescriptivism [1995], p.640)
Book Reference
'Cambridge Dictionary of Philosophy', ed/tr. Audi,Robert [CUP 1995], p.640
A Reaction
So that's an 'ought', but not a 'genuine ought', then? (No True Scotsman move). Someone ought to rescue that drowning child, but I can't be bothered.