 All parties agree that a speaker can use (17) to mean either [17a] or [17b]. Horn (1972) and Levinson (2000: 87–90) further agree with Carston that (17) itself is unambiguous. But whereas the neo-Griceans hold that (17) means [17a] rather than [17b], Carston (1988: 46–7) maintains that (17) means neither but can be used to say both. So the neo-Griceans hold that (17) always says [17a] while sometimes implicating [17b]. Carston holds that (17) is sometimes used to explicate [17a] and sometimes [17b]; neither is an implicature. The thesis that sentence meaning leaves open what is said to this extent is called semantic underdetermination.