It is clearly explained:

*What it is for a statement to be necessarily true,

*Why necessity, possibility, existence, and non-existence are properties of propositions (truths and falsehoods), not of objects or states of affairs,

*What conditions a class of expressions must meet if the expressions belonging to it jointly constitute a single language,

*The significance for meta-linguistic research of the concepts of systematicity and productivity, as Chomsky defines these terms, and the relevance of these concepts to researches into the nature of necessity,

*Why Quine's attempt to prove the non-existence of analytic truth is not only false but self-defeating,

and, finally,

*Why empirical science relies on truths of purely conceptual, non-observational kind to organize the data at its disposal.