Catherine A. Bradley, "Choosing a Thirteenth-Century Motet Tenor: From the Magnus liber organi to Adam de la Halle", in Journal of the American Musicological Society,  Vol. 72  No. 2, Summer 2019, pp. 431-492.

Abstract

This article explores trends and motivations in the selection of plainchant and vernacular song quotations as the foundations of thirteenth-century motets. I argue that particular tenor melodies that received only cursory treatment in the liturgical polyphony of the Magnus liber organi were adopted in motets on account of their brevity and simplicity, characteristics that enabled their combination with upper-voice song forms and refrain quotations.

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