\subsection{Poverty of stimulus arguments}
The best argument for innateness is the poverty of stimulus argument.
We need to step back and understand how poverty of stimulus arguments work.
Here I'm following \citet{pullum:2002_empirical}, but I'm simplifying their presentation.
How do poverty of stimulus arguments work? See \citet{pullum:2002_empirical}.
First think of them in schematic terms ...
Poverty of stimulus argument
\begin{enumerate}
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\item
Human infants acquire X.
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\item
To acquire X by data-driven learning you'd need this Crucial Evidence.
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\item
But infants lack this Crucial Evidence for X.
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\item
So human infants do not acquire X by data-driven learning.
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\item
But all acquisition is either data-driven or innately-primed learning.
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\item
So human infants acquire X by innately-primed learning .
\end{enumerate}
compare Pullum & Scholz 2002, p. 18
This is a good structure; you can use it in all sorts of cases, including the one about chicks' object permanence.
Now fill in the details ...
In our case, X is knowledge of the syntactic structure of noun phrases. (Caution: this is a simplification; see\citet[p,\ 158]{lidz:2004_reaffirming}).)
This is what the Lidz et al experiment showed.
Note that no one takes this to be evidence for innateness by itself.
What is the crucial evidence infants would need to learn the syntactic structure of noun phrases?
This is actually really hard to determine, and an on-going source of debate I think.
But roughly speaking it's utterances where the structure matters for the meaning, utterances like 'You play with this red ball and I'll play with that one'.
\citet{lidz:2003_what} establish this by analysing a large corpus (collection) of conversation involving infants.
What can we infer about innateness from this argument?
First, think about what is innate. The fact that knowledge of X is acquired other than by data-driven learning doesn't mean that X is not innate; it just means that something which enables you to learn this is.
Second, think about the function assigned to innateness. That which is innate is supposed to stand in for having the crucial evidence.
This, I think, is the key to thinking about what we *ought* to mean by innateness.
So attributes like being genetically specified are extraneous---they may be typical features of innate things, but they aren't central to the notion.
By contrast, that what is innate is not learned must be constitutive (otherwise that which is innate couldn't stand in for having the crucial evidence)