  Observation sentences are the starting point for our acquisition of knowledge, the child’s entry into cognitive language. They are also the sentences which are evidentially basic. What fits them to play both roles is that they are (largely) independent of other parts of our language. Hence they can (largely) be mastered by a child otherwise without linguistic competence, and known without presupposing other parts of our theory. (The reason for the qualification will become apparent at the end of this sub-section.)