Use of 'so'

"so" is a conjunction. similar to "and", "but" ,"or".

A conjunction is a joining word.

It can also be an averb. example- It was so big that it couldn't go through the door.

Welcome cdieoxide. I love your user name!

So in that context is in common usage I agree flyboy, but incorrect grammar I would feel.

It can be found in a similar though not exact use in Edna Ferber's award winning novel "So Big".

"So" can also be an adjective, as in, "I believe that is so."

Knowing your craft I wont argue with you Roberta.

However i still think its incorrect grammar.

I believe that is correct.

Double-checked before I posted, dadpad. It's correct usage, at least here in the US.

Another use of "so" as an adjective: "I cost twenty dollars or so."

I agree, this highlights that there is a a difference between American usage and Australian English which I think in some respects is more closely aligned with British.

Dadpad, is there an Australian dictionary as opposed to British O.E.D. or American Merriam-Webster; and if so what part or parts of speech does it list for "so"?

"It was so big that it couldn't go through the door." is perfectly good American or British English. "So" here, used as an adverb, means "to the extent or degree indicated or suggested"

"I believe that is so." is also correct American or British English. Here, used as an adjective, "so" means, "true as stated or reported; conforming with reality or the fact".

"Australian" English is more or less identical with British English. In fact the differences are mainly to do with vocabulary and slang. The grammar is 100% identical.

http://en.wikipedia.org/wiki/Australian_English

http://en.wikipedia.org/wiki/Australian_English_terms_for_people

http://www.nma.gov.au/play/aussie_english_for_the_beginner/

Us of "so"
I refer everybody to the newest book on grammar, Ben Yagoda's "When You Catch an Adjective, Kill It!". Chapter II, "Adverbs" cover various uses of "so" which basically define it as an adverb; see pp44, 57, (where he refers to it as an "intensifier"), and 58-60.