HCF differentiate (as we do) between aspects of language that are special to language (the “Narrow Language Faculty” or FLN) and the faculty of language in its entirety, including parts that are shared with other psychological abilities (the “Broad Language Faculty” or FLB).
The abstract of HCF makes the very strong proposal that the narrow language faculty “only includes recursion and is the only uniquely human component of the faculty of language.
Similarly (p. 1573), “We propose in this hypothesis that FLN comprises only the core computational mechanisms of recursion as they appear in narrow syntax and the mappings to the interfaces” (i.e. the interfaces with mechanisms of speech perception, speech production, conceptual knowledge, and intentions).
These assertions are largely independent: there may be parts of the narrow language faculty other than recursion even if the narrow faculty is the only part that is uniquely human; and the narrow faculty might consist only of recursion even if parts of the broad faculty are uniquely human as well).
But this interpretation is more strained, and is inconsistent with the preceding two quotations, which simply identify the narrow language faculty with recursion.
We agree that it is conceptually useful to distinguish between the language faculty in its broad and narrow sense, to dissect the broad language faculty into sensorimotor, conceptual, and grammatical components, and to differentiate among the issues of shared versus unique abilities, gradual versus saltational evolution, and continuity versus change of evolutionary function.
These suggestions, however, contradict their claim that the narrow language faculty “only includes recursion and is the only uniquely human component of the faculty of language.
They reconcile the contradiction by retaining the idea that the narrow language faculty includes only recursion but weakening the idea that only the narrow language faculty is uniquely human; specifically, they relegate word leaning to the broad language faculty.
So other than acquiring the names for salient things, it is hard to see how words can be carved away from the narrow language faculty and relegated to a generic mechanism that learns facts from people’s intentions.
Moreover, a good portion of people’s knowledge of words (especially verbs and functional morphemes) consists of exactly the kind of information that is manipulated by recursive syntax, the component held to make up the narrow language faculty.