Full Idea
Not every conclusion of moral deliberation expresses an obligation; for example, some moral conclusions merely announce that you 'may' do something.
Gist of Idea
Not all moral deliberations lead to obligations; some merely reveal what 'may' be done
Source
Bernard Williams (Ethics and the Limits of Philosophy [1985], Ch.10)
Book Reference
Williams,Bernard: 'Ethics and the Limits of Philosophy' [Fontana 1985], p.175
A Reaction
An important point for any deontological ethics. It may be possible to translate what 'may' be done into some form of duty, but it will probably involve contortions.