Full Idea
The 'conversational defence' of the truth-functional view of conditionals is that a conditional may not be assertible in difficult cases.
Gist of Idea
Conditionals are truth-functional, but unassertable in tricky cases?
Source
report of H. Paul Grice (Presupposition and Conversational Implicature [1977]) by Stephen Read - Thinking About Logic Ch.3
Book Reference
Read,Stephen: 'Thinking About Logic' [OUP 1995], p.69