When can we say that two distinct logical systems are, nevertheless, essentially the "same"? In this talk we discuss the notion of "sameness" between logical systems, bearing in mind the expressive power of their associated spaces of theories, but without neglecting their syntactical dimension. Departing from a categorial analysis of the question, we introduce the new notion of equipollence between logical systems. We use several examples to illustrate our proposal and to support its comparison to other proposals in the literature, namely Pollard's notion of homeomorphism, Pelletier's notion of translational equivalence (or synonymity), as well as with Post-equivalence, based on the definability of Boolean functions. This talk is on joint work with R. Gonçalves.