  Quine does not seem to have fully appreciated this point, though some of his later discussions come close to doing so (see, in particular, Quine 1996). It is not fatal to his general account; it complicates the story rather than requiring a radical change. There may be no sentences—at least none that satisfy the social criterion for observationality—which can be wholly mastered simply by acquiring appropriate dispositions to assent and dissent in response to current stimulations. For some sentences, however, acquiring such dispositions comes close to mastering their use, because those sentences are almost always true in those cases where observers receive sensory stimulations which dispose them to assent. (Clearly this will be a matter of degree.) So the acquisition of the relevant dispositions, and partial mastery of the sentence, can be used as a basis on which the child can learn more of the language, and more about the world. This further learning in turn allows the child to modify her or his original disposition to assent and dissent merely in response to current stimulation.