Language change involves the competition between alternative linguistic forms (1). When the forms evolve spontaneously, they either grow or decay monotonically (2, 3). In the case of the Spanish past subjunctive, the evolution of its two competing forms (ended in -ra and -se) was perturbed by the appearance of the Royal Spanish Academy in 1713, which enforced the spelling of both forms as perfectly interchangeable variants (4) at a moment in which the -ra form was dominant (5). Time series extracted from a massive corpus of books (6) reveal that this regulation in fact produced a renewed interest for the old form -se that eventually faded, leaving -ra again as the dominant one in the present day. We show that time series are successfully fitted by a two-dimensional linear model that integrates an imitative and a novelty component. The model reveals that the temporal scale over which collective attention fades is in inverse proportion to the verb frequency. The integration of the two basic mechanisms of imitation and attention to novelty allows to understand diverse competing objects, with lifetimes that range from hours for memes and news (7, 8) to decades for verbs. This suggests a general mechanism underlying cultural evolution.
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