  Many philosophers are content to take for granted the idea of an evidentially basic sentence. Quine, however, cannot take that attitude; he needs to show how we get “from stimulus to science”. The first step is to show that we can give a purely naturalistic account of how some linguistic utterances can be directly tied to the occurrence of stimulations of the sensory nerves---an account of observation sentences, more or less. Quine expends enormous labour on this point.