Another question I was asked concerns the interpretation of an utterance like “I want to get . get milk in it”.

There are two things here: First, at least when I looked at it, I took that to be a kind of disfluency, so I didn’t really treat this as two distinct instances of “get”. Rather, I interpreted this as basically just the sentence “I want to get milk in it.”

Second, is there a null subject? An overt subject? For this, I think the answer is: omit it from the computation. Clearly the verb “get” here does not have an overt subject. But, on the other hand, neither does it have one for adults. The sentence “I want to get milk in it.” is something that would be grammatical in an adult’s English as well, so it isn’t really a case of an ungrammatical null subject. (For an adult, this is one of those places where the subject is PRO, so it means something like “I want me to get milk in it.”) So, it’s misleading to count it as a null subject when what we’re looking at is the question of how many non-adult-like null subjects we find the child using, but it’s also not right to call it an overt subject.

The same thing, by the way, should hold of imperatives: “Get milk in it!” for example. Because here the distinction between null and overt subject is different (adults can, indeed must, have a null subject in imperatives), considering imperatives in the analysis would confuse the general point we’re trying to get at by looking at these utterances.