This seems an opportune time to note (doubtless unnecessary, but I'll
do it anyway) that this is a discussion that has been going on for
several decades now, and to post some relevant references (perhaps
useful; see refs at the end of this message). In particular, the
question of a center-embedding discontinuity was an active topic for
early investigation by a number of psychologists in the late 60s
through mid-70s; the most important papers in that regard are probably
Miller and Isard (1964) and of course the well known chapters by
Miller and Chomsky in Luce et al. (1963); papers like the one by de
Roeck et al. (1982) are a previous iteration of the discussion now
taking place on this list about whether such a discontinuity really
exists. Work by Church (1982), Pulman (1986), Abney and Johnson
(1991), Thompson et al. (1991), and Resnik (1992) is more explicitly
computational in nature, mainly focusing on the need to model apparent
processing limitations on center embedding while still allowing for
much less restricted left and right branching.
Although resurrecting the decades-old center-embedding issue on this
list may not in itself be particularly interesting (especially if
people simply reconstruct arguments that are already in most of those
old papers), it strikes me that there still might be something new and
interesting to contribute. First, I wonder whether searches in
spoken-language corpora could provide new evidence about
center-embeddings in a natural setting. In particular, this would
make it possible to get past this standard argument: (A) Look, here's
an Nth-order center embedding, and it's no problem! (B) Yes, but you
only say it's no problem because you were able to regress to previous
parts of the sentence while reading it.
Second, I am intrigued by Mark Johnson's suggestion that the
competence/performance distinction may somehow be rendered obsolete by
probabilistic grammars. (Though perhaps I am misinterpreting what he
wrote.) Certainly probabilistic grammars represent a way of encoding
both of what would traditionally be called a competence-level
description (the non-probabilistic structures of the grammar, defining
a space of combinatory possibilities) and a performance-level
description (the probabilities associated with different combinatory
operations), but even as someone who is somewhat skeptical of where
linguists traditionally draw the line between competence and
performance, I'm not sure that probabilistic grammars make that line
disappear. Rather, I think probabilistic approaches have the
potential to do something that (IMHO) should have been done a long
time ago: stop thinking of a complete competence theory as a
*prerequisite* to working on performance, and instead recognize that
the two are intimately connected. (Hawkins, 1990 has an interesting
take on this same point, though not from a probabilistic point of
view.)
Philip
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