Between Saying and Doing: From Lorenzen To Brandom and Back Mathieu Marion After a period of neglect, dialogical logic is now enjoying a revival, so its philosophical basis should be revisited. My aim here is merely to suggest the form of a rapprochement with Robert Brandom’s ‘inferentialism’. 1 One must therefore begin by separating dialogical logic from what I call here the ‘philosophy of the Erlangen School’, as one similarly free to separate intu- itionistic logic from Brouwer’s original philosophical stance. The basic ideas of dialogical logic were, as a matter of fact, put forward by Paul Lorenzen and Kuno Lorenz before the birth of the Erlangen School, with Lorenzen’s Ruf to Erlangen in 1962. 2 The ensuing collaboration with Wilhelm Kamlah resulted in the School’s ‘Bible’, Logische Prop¨ adeutik [16], which sets forth a philosophy of language and logic meant to provide foundations to dialogical logic. 3 There are reasons not to be satisfied with it – I have already given some arguments in [26], to which I shall not come back here. My sugges- tion is simply to hive off the logic from its philosophical basis and then to ‘graft’ it on Brandom’s ‘inferentialism’. As it stands, this suggestion is, how- 1 I am here developing a little bit further an idea first put forth in [5, p. 260] and [26, p. 19-21]. 2 Dialogical logic was first proposed in [21], and further developed in particular in Lorenz’s doctoral dissertation (under Lorenzen’s supervision) at Kiel in 1961, now re- produced along with Lorenzen’s original papers and other key papers in [24, p. 17-95]. The introduction of concepts from game theory are among the innovations in Lorenz’s dissertation. It can be argued that Lorenzen actually introduced dialogical logic quite independently from possible motivations arising from the ‘philosophy of the Erlangen School’, in order rather to solve problems raised by his earlier attempt at providing ‘op- erative’ foundations of logic and mathematics in [20] (on this, see [18] and [2, p. 237]). Of course, the two are not unrelated, since Hugo Dingler – see, e.g., his Philosophie der Logik und Arithmetik [8] – is one of the precursors, with Herman Weyl, to Lorenzen’s original ‘operational’ standpoint in the foundations of mathematics [20, p. 31] & [10, p. 10]. Furthermore, Dingler’s ideas were further developed within the Erlangen School. Nevertheless, it remains that the key ideas of dialogical logic – the definition of logical connectives in terms of rules for non-collaborative games between two persons, along with the definition of truth in terms of the existence of a winning strategy – are not to be found in Dingler. 3 Further English-language presentations are also found in Lorenzen’s John Locke Lectures for 1967 [22] and in Constructive Philosophy [23].