The notions of identity and indistinguishability are a frequent source of misunderstanding, even among researchers working within the same field. The present text is primarily didactic in intent: it aims to show that a large part of such disagreements concerns the association of different meanings with one and the same word. Six notions are introduced and articulated – qualitative identity and numerical identity, haecceity, operational distinguishability, genidentity and permutational indistinguishability – and their content is clarified by examining two paradigmatic examples in parallel: two quantum particles and two occurrences of a word in a text. It is argued that the monadic version of Leibniz’s principle of the identity of indiscernibles is violated both by bosons, which can occupy one and the same state, and by fermions, for which indistinguishability operates in spite of Pauli’s exclusion principle, as the statistical counts make evident; the status of weaker relational versions of the principle remains contested. In the concluding part, the linguistic example is reread in the light of the conceptuality interpretation of quantum mechanics, for which it ceases to be merely an analogy and becomes a genuine explanation: on this interpretation, absent information can signify an absence of reality rather than mere ignorance.

[In preparation]