A unified theory of language and grammar might suggest that there is a base level of innate grammar that belongs to the structures of mind such as notions of agency, causality and intentionality. So that all sentences have a subject which causes an action with or without intentionality. Grammatical language works like this because rational mind works like this.
However layered on top of this we might have more functional grammar such as 'he' 'she' 'we' 'one' 'you' which can change according to social register and category such a gender. Verb grammar can change socially also in that verb endings and tenses are shaped socially rather than set in the mind but the notion of tense itself may well be set in the mind in terms of the passage of time. Could we then say that at base Grammar with a capital 'G' is mind base whereas functional grammar (small 'g' ) at the surface is socially shaped? Therefore the nativist and constructivist perspectives can be combined and layered? What do you think? Please advise on this research related question? Thankyou. Dave