At an early stage of acquisition the utterances children produce consist of only two words. Can these two word utterances be seen as syntactically or semantically analysed in any way? How productive is the Pivot theory?
Yes. I was deeply impressed by the reports of vertical constructions by Ron and Suzy Scollon in the '70s. Here is a discussion by Charlene Sato of that and other relevant work: The Syntax of Conversation.