Abstract

The usual approach to validity holds that an argument is valid in virtue of its form. This idea has been developed along two main lines: model-theoretic and proof-theoretic. Both frameworks presuppose a distinction between logical and non-logical vocabulary. This chapter introduces these two conceptions of validity and discusses their respective approaches to the demarcation question. We review two versions of the overgeneration challenge for the model-theoretic account, formulated in terms of isomorphism invariance. Similarly, we review two challenges faced by the proof-theoretic account, formulated in terms of the logical vocabulary’s inferential role. The chapter thus offers a comparative overview of the model-theoretic and proof-theoretic conceptions of formal validity.