This commentary concerns two issues: the contribution of connectionism and theories of learning to developmental psychology; and the status of connectionist models of syntax acquisition.

Previous research indicates young children are likely to interpret the surface-structure subject of a sentence as the deep subject regardless of syntax, e.g. John is chosen as subject of both John is easy to please and John is eager to please. However, with one-noun sentences, the task required both recognizing a difference between the sentences and inferring an implied noun. Thus an inability to make an inference might be responsible for the children's consistency in choosing the surface subject. Two experiments compared kindergarteners' interpretations of one- and two-noun sentences. With two-noun sentences (i.e. John is easy for Jim to please), which explicitly stated the surface object, consistency in choosing the surface subject decreased.

Thai has imperfective aspectual morphemes that are not obligatory in usage, whereas English has obligatory grammaticized imperfective aspectual marking on the verb. Furthermore, Thai has verb final deictic-path verbs that form a closed class set. The current study investigated if obligatoriness of these grammatical categories in Thai and English affects the expression of co-occurring temporal events and actions depicted in three different short animations. Ten children aged four years, five years, six years and seven years, and ten adults as a comparison group from each of the two languages participated. English speakers explicitly expressed the ongoingness of the events more than Thai speakers, whereas Thai speakers expressed the entrance and exit of protagonists depicted in the animations significantly more than English speakers. These results support the notion that obligatory grammatical categories shape how Thai and English speakers express temporal events or actions.

The review article by Sabbagh & Gelman (S & G) on The emergence of language (EL) mentions several criticisms of strong emergentism, the view that language emerges through an interaction between domain-general learning mechanisms and the environment, without crediting the organism with innate knowledge of domain-specific rules, a view that successful connectionist modelling is taken to support. One criticism of this view and the support for it that connectionist modelling putatively provides has been made frequently, and is noted by S & G: it is arguable that connectionist simulations work only because the input to the network in effect contains a representation of the knowledge that the net seeks to acquire. I think it is worth adding to this another criticism that to my mind is a fundamental one, but which has not featured so strongly in critiques of connectionism. A primary goal of modern linguistics has been to account not merely for what patterns we do see in human languages, but for those that we do not. The concept of Universal Grammar is precisely a set of limitations on what constitutes a possible human language. The kind of example used in teaching Linguistics 101 is the fact that patterns of grammaticality are structurally, not linearly, determined: in English we form a yes–no question by inverting the subject NP and auxiliary verb, not by inverting the first and second words of the equivalent declarative sentence, or the first and fifth words, or any number of conceivable non-structural operations. Could a connectionist mechanism learn such non-structural operations? Perhaps I have asked the wrong people, but when I have queried researchers doing connectionist modelling, the answer appears to be ‘yes’. If that's the case, then connectionist mechanisms as currently developed do not constitute an explanatory model of human language abilities: they are too powerful.