The most basic property of human language is that in each of its variants, it provides an unbounded array of hierarchically structured expressions that receive interpretations at two interfaces, sensorymotor for externalization and conceptual-intentional for mental processes. A central problem, then, is to determine the nature of the recursive procedures that have this property. General scientific norms direct inquiry to the simplest possible solution – minimal recursion – to deepen explanatory power and expedite the study of language acquisition, and to offer some hope for some eventual insight into evolution of the language capacity. Pursuit of this objective has led to elimination of many unwanted stipulations and also grounding some fundamental properties of universal grammar. Among other consequences, it provides evidence for an asymmetry of the interfaces, with externalization an ancillary procedure, a conclusion consistent with well-known properties of language and the very limited evidence about evolution.