The historic relation between Frege and ‘Frege’s principle’ is investigated. What did Frege intend with the principle, did he change his opinion concerning it, did he invent the principle? Johan van Benthem did twenty years ago reseach on another aspect of Frege’s work and some of his opinions are confirmed by the present research. His pregnant formulations and suggestive metaphors are quoted w...

This paper is a contribution to our understanding of the relationship between uniform and nonuniform proof complexity. The latter studies the lengths of proofs in various propositional proof systems such as Frege and bounded-depth Frege systems, and the former studies the strength of the corresponding logical theories such as VNC1 and V0 in [7]. A superpolynomial lower bound on the length of pr...

One particular topic in the literature on Frege’s conception of sense relates to two apparently contradictory theses held by Frege: the isomorphism of thought and language on one hand and the expressibility of a thought by different sentences on the other. I will divide the paper into five sections. In (1) I introduce the problem of the tension in Frege’s thought. In (2) I discuss the main atte...