Full Idea
In its unquantified form 'If p then q' the indicative conditional is perhaps best represented as suffering a truth-value gap whenever its antecedent is false.
Clarification
A 'truth-value gap' is 'neither true nor false'
Gist of Idea
Normal conditionals have a truth-value gap when the antecedent is false.
Source
Willard Quine (Word and Object [1960], §46)
Book Reference
Quine,Willard: 'Word and Object' [MIT 1969], p.226
A Reaction
That is, the clear truth-functional reading of the conditional (favoured by Lewis, his pupil) is unacceptable. Quine favours the Edgington line, that we are only interested in situations where the antecedent might be true.