This article investigates some functions of the determinative sum(e) in Old, Middle and Early Modern English. It traces, quantifies and models the diachronic development of sum(e) as a pre-head element from a usage-based, cognitive Construction Grammar perspective by postulating several semi-specified but also abstract constructional OE and ME NP-schemas and sketching the observable (changing) network (re)configurations. By analyzing texts from the Penn–Helsinki Parsed Corpus of Middle English (PPCME) and the Penn–Helsinki Parsed Corpus of Early Modern English (PPCEME), the article especially focuses on the demise of the so-called ‘individualizing’ usage with singular nouns and traces the incipient stages of sum(e) as an indefinite near-article with plural and mass nouns. R was used to calculate correlation coefficients and measures of statistical significance in univariate analyses, and for multivariate regression models to address questions involving more than one predictor variable. It is shown that the usage of sum(e) with singular nouns became marginalized because of constructional competition with the numeral ān. In Old English, the two forms were both occasionally used to mark indefiniteness before singular nouns, but ultimately ān became the default marker of indefiniteness ousting sum(e). We also show that that the usage of sum(e) as an indefiniteness marker for plural nouns increased drastically from the later ME period onwards, particularly in informal text genres. Moreover, from the earliest periods onwards, there is a strong preference for this function to occur with complex NPs with pre- and post-head modification, which seem to have acted as bridging contexts.