What is secondary grammaticalization? Trying to see the wood for the trees in a confusion of interpretations

Abstract Over the years, several studies on grammaticalization have used the contrasting terms primary and secondary grammaticalization for, roughly speaking, changes from lexical to grammatical and from grammatical to (more) grammatical. Primary grammaticalization has been treated as instantiating prototypical grammaticalization. This article scrutinizes the concept of secondary grammaticalization with the goal of assessing whether it has explanatory power and encompasses processes of grammaticalization that are sufficiently different from primary grammaticalization to justify distinct terminology. In the first part of the article, I take stock of the different definitions and interpretations of the concept of secondary grammaticalization in the literature. I conclude from this review that there is no unified definition and that the concept has in fact been applied to an array of widely differing changes. In the second part, I take a closer look at five distinct interpretations, which together cover the spectrum of phenomena featuring in the literature, in order to assess their explanatory power and relevance. The conclusion from this exercise is that the changes identified in each of the five definitions can be captured within a general definition of grammaticalization, and neither of them necessitates the addition of secondary grammaticalization as a separate notion.