This case study reconstructs the grammaticalization paths of middle, midst and process, which led to a set of progressive aspect markers (PAMs) in Present-day English. The three PAMs developed from two different source structures, viz. complex prepositions in the middle/midst of + NP and complex appositive noun phrase the process of + NP. The main theoretical aim of the diachronic reconstruction is to identify and characterize the main mechanisms of change that affected the different structures with these nouns on their grammaticalization trajectories: (i) reanalysis in the sense of functional reparsing of an existing structure; (ii) analogization: the attraction of new functional properties to an existing structure; (iii) neo-analysis by analogy: the creation of a functional structure that is new in the item’s trajectory of change. We also discuss how these mechanisms of change interact with enabling factors such as metaphor and metonymy, collocational fixation, expansion and reclustering, and discursive functions.