It is usually stated that quantum mechanics presents problems with the identity of particles, the most radical position—supported by E. Schrödinger—asserting that elementary particles are not individuals. But the subject goes deeper, and it is even possible to obtain states with an undefined particle number. In this work we present a set theoretical framework for the description of undefined particle number states in quantum mechanics which provides a precise logical meaning for this notion. This construction goes in the line of (...) solving a problem posed by Y. Manin, namely, to incorporate quantum mechanical notions at the foundations of mathematics. We also show that our system is capable of representing quantum superpositions. (shrink)

David Lewis may be regarded as an antiessentialist. The reason is that he is said to believe that individuals do not have essential properties independent of the ways they are represented. According to him, indeed, the properties that are determined to be essential to individuals are a matter of which similarity relations among individuals are salient, and salience, in turn, is a contextual matter also determined to some extent by the ways individuals are represented. Todd Buras argues that the acknowledgment (...) of natural properties in counterpart theoretic ontology affects Lewis’s theory with regard to essentialism. Buras’s reasoning is appealing. He claims that, since natural properties determine the existence of similarity relations among individuals that are salient independent of context, Lewis can no longer be claimed to be an antiessentialist. The aim of this paper is to argue, against Buras, that if counterpart theory was antiessentialist before natural properties were taken into account, then it remains so afterwards. (shrink)

It is usually stated that quantum mechanics presents problems with the identity of particles, the most radical position—supported by E. Schrödinger—asserting that elementary particles are not individuals. But the subject goes deeper, and it is even possible to obtain states with an undefined particle number. In this work we present a set theoretical framework for the description of undefined particle number states in quantum mechanics which provides a precise logical meaning for this notion. This construction goes in the line of (...) solving a problem posed by Y. Manin, namely, to incorporate quantum mechanical notions at the foundations of mathematics. We also show that our system is capable of representing quantum superpositions. (shrink)