The Discontinuity Model (DM) described in this article proposes that adults can learn part of L2 morphosyntax twice, in two different ways. The same item can be learned as the product of generation by a rule or as a modification of a template already stored in memory. These learning modalities, which are often seen as opposed in language theory, integrate and superpose in adult SLA. Learners resort to grammatical rules and statistical templates under different circumstances during language processing. Ontogenetically, while in L1 acquisition, the natural endowment for language constrains statistical learners' capacity by narrowing the hypothesis space; in adult SLA, statistics can reopen the window of opportunity for grammar and drive adult learners to derive part of L2 morphosyntax. This article proposes a computational and psycholinguistic model of how this might occur. According to this model, skewness between transition probabilities (TP) represents the triggering factor in both L1 and L2 acquisition. As fluctuation in TP drives children to individuate the words in a speech stream, so skewness between TP drives adult learners to discover the grammatical features that are hidden in asymmetric chunks.