# Canonical lists and optional arguments

**URL:** <https://delphinqa.ling.washington.edu/t/canonical-lists-and-optional-arguments/524>\
**Category:** Grammar Matrix\
**Created:** [July 4, 2020, 1:13am UTC](https://delphinqa.ling.washington.edu/t/canonical-lists-and-optional-arguments/524 "2020-07-04T01:13:56Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![olzama](https://delphinqa.ling.washington.edu/user_avatar/delphinqa.ling.washington.edu/olzama/32/6_2.png) [@olzama](https://delphinqa.ling.washington.edu/u/olzama)\
**Post date:** [July 4, 2020, 1:13am UTC](https://delphinqa.ling.washington.edu/t/canonical-lists-and-optional-arguments/524/1 "2020-07-04T01:13:57Z")

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Maybe someone who is more comfortable with the hierarchy could help me.

We introduced this new list type for non-gappy things (see [here](https://delphinqa.ling.washington.edu/t/in-situ-wh-words-in-languages-which-also-do-extraction/394/27)). And that’s fine, I can use that in some languages sometimes, and it helps.

But I am looking now into possibly just using it always in head-adjunct rules, because, conceptually, it kind of should work across the board I think.

But I am not sure what to do about dropped arguments here. Something like a head-opt-subj rule requires an _unexpressed-reg_ as the subject on the head daughter and that one is _non-canonical_.

Is there some cross type I could actually use here, must _unexpressed_ also be _non-canonical_? I am getting lost in the hierarchy a bit.

To summarize, I want a type that means: the argument can be dropped, or we are still looking for it, or it was successfully attached, but it can’t be a _gap_.