Full Idea
If we say that a man is a free agent in proportion as he acts rationally, we cannot also say that it is by free choice that he acts irrationally.
Gist of Idea
If we say that freedom depends on rationality, the irrational actions are not free
Source
Henry Sidgwick (The Methods of Ethics (7th edn) [1874], p.511), quoted by John Kekes - Against Liberalism 7.4
Book Reference
Kekes,John: 'Against Liberalism' [Cornell 1997], p.153
A Reaction
A very nice riposte. Clearly people can rationally choose to act irrationally, e.g. at a wild party.
Related Idea
Idea 19922 People are only free if they are guided entirely by reason [Spinoza]