Full Idea
Paradox: no course of action could be determined by a rule, because every course of action can be made out to accord with the rule. Answer: if everything can accord with the rule, then everything can conflict with it, so there is no accord or conflict.
Gist of Idea
Every course of action can either accord or conflict with a rule, so there is no accord or conflict
Source
Ludwig Wittgenstein (Philosophical Investigations [1952], §201)
Book Reference
Wittgenstein,Ludwig: 'Philosophical Investigations', ed/tr. Anscombe,E. [Blackwell 1972], p.81
A Reaction
This is a very interesting claim which goes beyond the private language question. It seems to imply, for example, Dancy's 'Particularism' about morality, which is a general rejection of rules and principles in moral thought.