Relations that are seldom or never signaled

[Alistair Knott]

Here are some more worms from the `multiple levels of relations' can.

First, I'd like to apologise to Bill Mann for misrepresenting RST's
position on multiple simultaneous relations and tree-shaped text structure
diagrams. Bill says:

> In RST as I understand it, the analyst can affirm more than just a simple
> tree-forming set of relations.

I'm glad to get this misconception out of the way, because (as Bill
mentioned) lots of people have understood RST as proposing that a single
tree-shaped structure of relations (or more accurately, of schema
applications) is sufficient for the analysis of every coherent text. I had
always thought that this was one of the theory's strongest attractions:
the way I understood it, it was making a very strong and simple claim
about the nature of text coherence, and stimulating a very productive
research programme centred around the testing of this claim.

Anyway, to recap: the multiple levels issue came up as a result of a
discussion we were having about the relationship between connectives and
relations. The idea that I'm pushing is that we should posit a strong
relationship between connectives and relations, so that tests to do with
inserting connectives in particular contexts can be used as concrete
diagnostics for the presence of particular relations. Bill Mann said he was
happy to use connectives as part of the decision procedure about which
relation applies, but still doesn't want to use them as a way of defining
which relation applies.

We can imagine placing theories of discourse structure on a continuum of
`specificity'. At one end of the continuum, we have a theory that says
that a coherent text can be analysed by a single tree-like structure of
relations, where relations can be defined by concrete tests that relate to
surface signals.  At the other end of the continuum, we have a theory that
says (a) that on top of the tree-like structure we have to allow that
several relations may apply simultaneously between two given text spans,
(b) that relations may hold between non-adjacent text spans, and (c) that
there are no simple surface-based tests to determine the presence or
absence of relations. The theory at the `specific' end of the continuum is
quite readily testable, and probably `more simple than possible' (to quote
John Bateman quoting Einstein). The theory at the `nonspecific' end of the
continuum is very hard to test in the first place.  It seems to me that
the way to progress is to start off with a very specific theory, find out
where it goes wrong, and then look for the simplest and most tightly
specified alternative theory that remedies the problem. My complaint about
positing multiple levels of relations is that seems like too big a jump
towards the nonspecific/unfalsifiable end of the continuum.

For what it's worth, here are two jumps away from the most specific end of
the spectrum that I would advocate. Judge for yourselves how far I'm
jumping!

1) As Bill noted in his original posting in this thread, there are some
   relations that are seldom if ever signalled by a connective. I suggested
   that ELABORATION and BACKGROUND were the two principal offenders. Rather
   than abandoning the mapping between relations and connectives, I suggested
   that ELABORATION and BACKGROUND should be treated as exceptions, which are
   better modelled using the entity and NP-based metaphor of focus, which is
   needed for independent reasons in a theory of coherence.

2) The set of connectives is itself hierarchically structured: there are some
   very general connectives, like `and', `so', `then' and so on, which have
   different meanings in different contexts, Rather than treating such
   connectives as lexically ambiguous words with unrelated senses, I argued
   that all relations that can be signalled by a given general connective
   have some semantic component in common. The idea is that connectives
   don't necessarily signal whole relations, but rather signal components of
   relations. The model that results is one where relations are thought
   of as composite constructs, defined in terms of the values of a
   number of orthogonal parameters. This model has something in common
   with a model that  allows multiple simultaneous relations. But it
   still makes quite concrete predictions about the relationship between
   connectives and relations.

Anyway, there are a couple more worms for your perusal!

Ali