I show that propositional intuitionistic logic is complete with respect to an adaptation of Dummett’s pragmatist justification procedure. In particular, given a pragmatist justification of an argument, I show how to obtain a natural deduction derivation of the conclusion of the argument from, at most, the same assumptions.

We examine the proof-theoretic verificationist justification procedure proposed by Dummett. After some scrutiny, two distinct interpretations with respect to bases are advanced: the independent and the dependent interpretation. We argue that both are unacceptable as a semantics for propositional intuitionistic logic.

Dummett’s justification procedures are revisited. They are used as background for the discussion of some conceptual and technical issues in proof-theoretic semantics, especially the role played by assumptions in proof-theoretic definitions of validity.

O objetivo deste texto é discutir a tarefa filosófica de elucidação do conceito de conseqüência lógica. Primeiramente, serão eleitos dois critérios de adequação para uma elucidação desse conceito: (1) preservação da verdade nas instâncias, ou adequação material e (2) garantia da verdade da conclusão na inferência válida, ou adequação epistêmica. Em seguida serão apresentadas a proposta de Tarski (1956) e as correspondentes críticas de Etchemendy (2008). Conclui-se com comentários a respeito da natureza das investigações lógicas.

The dissertation provides an analysis and elaboration of Michael Dummett's proof-theoretic notions of validity. Dummett's notions of validity are contrasted with standard proof-theoretic notions and formally evaluated with respect to their adequacy to propositional intuitionistic logic.