This monograph presents the first comprehensive diachronic account of copular and passive verb constructions in Old and Middle English. Peter Petr analyzes:
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is 'is' and bið 'shall be, is generally' into a single suppletive verb, and how it is related to the development of a general analytic future shall be.

In explaining each of these changes, Petr
Using a radically usage-based approach, treating syntax as emerging from (changing) frequencies, draws attention to general principles of constructional change, including but not limited to grammaticalization and lexicalization. He proposes novel parallelisms between linguistic and ecological evolution. Going beyond the view of language change as propagating only in social interaction, Petr explains how each individual's mental grammar can be seen as a dynamic ecosystem with hierarchical environments (clausal niches, textual habitats). In this view, the interconnectedness of seemingly unrelated changes, itself resulting from cognitive economy principles, is arguably more decisive in lexical change than is functional competition.