This volume develops a theory of meaning and a semantics for both mathematical and empirical sentences inspired to Chomsky’s internalism, namely to a view of semantics as the study of the relations of language not with external reality but with internal, or mental, reality. In the first part a theoretical notion of justification for a sentence A is defined, by induction on the complexity of A; intuitively, justifications are conceived as cognitive states of a particular kind. The main source of inspiration for this part is Heyting’s explanation of the intuitionistic meaning of logical...