Since the beginning of the twentieth century, prominent authors including Jean Piaget drew attention to Edmond Goblot's account of mathematical thought experiments. But his contribution to today's debate has been neglected so far. The main goal of this paper is to reconstruct and discuss Edmond Goblot's account of "logical operations" (the term he used for thought experiments in mathematics) and its interpretation by Piaget against the theoretical background of two open questions in today's debate: 1) the relationship between empirical and mathematical thought experiments, and 2) the question of whether mathematical thought experiments can play a justificatory function in proofs.The main corollary of this analysis is that Piaget's interpretation is seriously flawed and insufficiently appreciative of important theses of Goblot's account. First, Goblot can be easily defended against Piaget's main criticism, and secondly, Goblot developed ideas about mathematical thought experiments that still deserve attention. KEYWORDS: mathematical thought experiments; mathematical vs empirical knowledge; psychology vs logic of knowledge; Goblot Edmond; Piaget Jean; Rignano Eugenio; Chaslin Philippe. authors such as André Lalande and Jean Piaget would later call attention not only to Eugenio Rignano 1 and Edmond Goblot 2 , but also to Philippe Chaslin 3 , and discuss their main theses.However, these authors have been forgotten, and are not now referenced in the current debate on the epistemological and methodological status of TEs.The neglect of these authors would be worth explaining since two well-known authors, Lalande and Piaget, discussed their ideas in well-known works. Lalande not only called attention to Goblot in 1919a and 1919b, but also in his famous and commonly used Vocabulaire technique et critique de la philosophie (1932), where he included the entry "Expérimentation mentale" (French translation of Ernst Mach's Gedankenexperiment). With special reference to the first chapter of "Rignano, Psychologie du raisonnement" (Rignano 1920) and to the eleventh chapter of "Goblot, Traité de logique" (Goblot 1918), he notes that "[t]his expression, and, moreover, the analysis of the operation which it designates, have become very usual." (Lalande 1932, Tome III). Piaget drew attention to and discussed Edmond Goblot, Eugenio Rignano and Philippe Chaslin's accounts of TEs beginning in 1922, in direct connection with mathematical reasoning and TE ("expérience mentale"). 4 Still, these authors, as well as Piaget's own theory of TEs (which he developed in the course of his critical discussion with these authors), have also been unduly neglected so far, both in the general context of today's debate on TEs and specifically with respect to MTEs. However, it is not my purpose to explain this historiographical neglect, nor it is possible, for reasons of space, to discuss all the authors mentioned. Instead, this paper, starting from Piaget's interpretation and criticism, will focus on Edmond Goblot's account of "logical operations" (the ...