Inconsistency, Quasi-Truth, and Physics Newton C. A. da Costa and Décio Krause Department of Philosophy Federal University of Santa Catarina 88040-900 Florianópolis, SC – Brazil ncacosta@terra.com.br, deciokrause@gmail.com February 4, 2011 Abstract In this work we study the nature of informal inconsistencies in physics, focusing mainly on the foundations of quantum theory, and appealing to the concept of quasi-truth. We defend a pluralistic view of the philosophy of science, grounded on the possibility of the existence of inconsistencies, and on the notion of quasi-truth. Here, we treat only the ‘classical aspects’ of the subject, leaving for a forthcoming paper the ‘non-classical’ part. Thus, despite in the opening section we consider a rather wide category of incon- sistencies, not all of them take part of the final discussion. 1 Introduction We begin by distinguishing between inconsistencies within a certain formal sys- tem (formal inconsistencies) and what we call informal inconsistencies. The for- mer, as its name indicates, appear when we have two theses α and ¬α in a suitable formal system whose language contains a symbol of negation, ¬. The informal inconsistencies are difficult to characterize, but they can be roughly classified in two groups: the real inconsistencies and the semiotic ones [6, pp.204-5]. Semiotic inconsistencies may be thought of as expressing certain incompatibilities between concepts, assertions, hypothesis, or even theories, and arise from semiotic factors of either syntactical, semantical, or pragmatical nature. The real ones are linked 1