@Jasper - Firstly, humble apologies for misidentifying you. I'd been having a bit of a discussion with jayles recently and got confused.

Secondly, to the nitty gritty. I have no problem with "so that" as a subordinator / subordinating conjunction (and you could also have "in order that"), but I couldn't think how "that" would be used alone in this meaning. (But see further on).

Googling "subordinator of purpose" mostly seems to only bring up "so that" . Most (of the not very many) sites I've looked at don't seem to list "that" as a subordinator, YourDictionary, however, does (but without an example, unfortunately). Furthermore, an academic paper I came across suggested (that) "that" was used this way in Old English.

There are also other constructions with "so ... that", as in "She was so tired (that) she went to bed" - does that count as a subordinator? I think it probably does, even though it comes at the end of the subordinate clause rather than at the beginning. It expresses reason rather than purpose, of course. And it appears that this is another example where we can omit "that".

Talking of which, (and going back to the original question) Oxford Advanced Learner's Dictionary suggests that we are more likely to omit that in that (noun) clauses when it
follows a reporting verb or adjective, but less likely to do so when it follows a noun, as in "The fact (that) he's older than me is not relevant."

https://www.dlsweb.rmit.edu.au/lsu/content/4_writingskills/writing_tuts/linking_LL/subordinators.html

OK, Jasper, I've found some, with obligatory (apparently) may/might:

"We eat that we may live."
"He ate that he might not die."

http://www.englishpractice.com/improve/sequence-tenses/

But these don't sound very natural to me, and when I Google "that he may", in this sense, I get mainly passages from the Bible - "For I have chosen him, that he may command his children and his household after ..." - But I think it sounds rather old-fahioned. There are several examples in one paragraph in this translation of the eighteenth century "The System of Nature":

http://books.google.pl/books?id=h50d39hfIAoC&pg=PA11&dq=%22that+he+may%22&hl=en&sa=X&ei=MuF8UZiYFI3EPKLFgeAI&redir_esc=y#v=onepage&q=%22that%20he%20may%22&f=false

Just to mention that the verb reference has another meaning, where I don't think "refer" could be substituted. I wonder if this could be the older meaning (it is the one the dictionary lists first):

provide (a book or article) with citations of sources of information - "each chapter is referenced, citing literature up to 1990" (Oxford Dictionary Online). Oxford also lists the use of "reference" in the meaning of "refer to" as formal, as would be suggested by its use in these US government documents from 1969:

http://books.google.pl/books?id=pgw_BIRkMj8C&pg=PA615&dq="referenced"&hl=en

There are very few examples of "reference" as a verb in the British National Corpus, but here are a couple where I really don't think "refer" would work:

"Each number on the cost statement is referenced to a note."

"Nadir pressure was referenced to the prevailing midoesophageal body pressure"

But this presumably means something like "cross-referenced". In the next example, on the other hand, "refer" could no doubt easily be substituted, and that "to" seems a bit unnecessary to me. Sounds as though they couldn't decide which to use:

"the letter of confirmation that we reference to because it was a repeat"

porsche et al are of course right about trolling being a type of fishing (although I confess I had to check a dictionary, as this seems to be more of a North American usage). Hence the meaning of to search for something - "politicians trolling for votes", as well as the newer meaning that KWM explained (also given at Oxford Online).

Incidentally, there is another British meaning of "troll" as a verb- "walk, stroll", probably from Polari, a kind of cant slang, some of whose word were made famous by Kenneth Williams and Hugh Paddick on "Round the Horne". "Look who's trolling in!"

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

Google site searches of both American and British newspapers would suggest that use of comma or no comma before "respectively" is fairly evenly divided.

One editing blog suggests it's context specific - "If the sentence is long and has many parameters, then use the comma for clarity. If not, the comma may be omitted". And he adds there is no difference between AmE and BrE here. Seems a sensible approach to me.

http://blog.editage.com/taxonomy/term/350#.UXWZdkrQWM4

@Stu_ck - it seems to me that something similar happens with the expression "begs the question". It's original use in logic is very precise, but not obvious from the words themselves - something vaguely similar to a circular argument, I think. Meanwhile the rest of us use it in a different way, much closer to the literal meaning of the words, something like "suggests or demands the question", usually followed by "of ...".

Only a tiny minority know of the original meaning, let alone use it, but you get a few people being hyper-critical of those of us who use it in its more popular meaning. But there's no reason why both can't co-exist. I find it a kind of intellectual snobbery, really.

There is nothing surprising in psychologists using unconscious and subconscious in a different way from the rest of us: there is often a difference between the way specialists and lay people use certain words. "Classical music", for example, means something different to a musical historian than to the general public. Should I say that anybody using the term to apply to anything except a certain style of music composed between c1750 and c1820 is using it "incorrectly"? Of course not!

For the minority to insist that the majority are wrong because we don't understand the finer points of some arcane debate, is for me, to misunderstand how language works.

Mind you, it even happens with linguists. I read an article recently by a prominent linguistics professor lambasting people who say that an adjective "is a word that describes a noun", calling them " twaddle-repeaters". His point being that they "modify" nouns, but "describe" things denoted by those nouns. However true, I think that is a technicality that would escape most non-grammar freaks. (Oxford defines adjective as "a word naming an attribute of a noun, such as sweet, red, or technical.")

His own definition of an adjective is - "A category of lexemes characteristically denoting properties of persons or objects (old, big, round. blue, good). The prototypical adjective can be used both attributively and predicatively (hot soup, The soup is hot), participates in the system of grade (occurs in the comparative and superlative), and takes adverbs as modifier (extremely hot, very useful)." Totally accurate, but I don't think I'll try it on my students just yet.

@James C - Bravo. :) But naturally, we should all continue with whatever feels most comfortable (I'm really not sure which I use, or even if I'm consistent).

And you're in good company, by the way. An editor and professor of English admitted recently that for twenty years or so she has been marking students and writers wrong for writing "on the other hand" without a corresponding "On the one hand", and has just realised she's been wrong all along. (It turns out that we use "on the other hand" far more often without than with).

http://languagelog.ldc.upenn.edu/nll/?p=4573

@jayles - By the way, although I have withdrawn from the fray, I still keep an eye on the Anglish page, and your Newcastle song would be perfectly understandable to any Scot. "Haud yer whisht" is very common for "be quiet", even among speakers of standard Scottish English.

@jayles, when "that" starts a noun clause (i.e. a "that" clause), as in your first example, I would suggest (that) it's a conjunction, not a relative pronoun. It's only a relative pronoun when it introduces a relative clause (what some would call an adjective clause).

Basically, we can only omit "that" when it starts a clause. As far as I can see, that means nearly always with a that clause (noun clause), unless, as in jayles' second example, the "that" clause is the subject. Oxford Advanced Learner's Dictionary puts
"that" in brackets in all its examples of "that" clauses where it is not the subject.

And it means under certain conditions with a relative clause (as outlined in my earlier comment). But "that" can't be omitted in jayles' example about the dog, because it refers to the subject of the verb in the relative clause ("ate"). On the other hand, in "This is the neighbour (that) my dog ran at." - "that" refers not to the subject, but to the object of the preposition "at", so can be omitted.

I don't think "that" can be used as a conjunction to introduce an adverb clause,
but it can certainly be used as an adverb, modifying an adjective - "Come on! The film wasn't that bad", or another adverb "It can't be that far now", and in British idiomatic use to mean something like "so" - "I was that knackered (exhausted), I couldn't go another yard", "We were that close to winning".

So we have 5 uses of that, in only two of which can it be omitted.

Conjunction in "That" clauses - "She said (that) she would be late."
Relative pronoun in restrictive / defining relative clauses - "This is the house (that) I was talking about."
Demonstrative pronoun - "That's just what I said."
Demonstrative determiner - "That meal was delicious."
Adverb - as above

@Kay K - some might disagree, but I think Brits count as native speakers. :))

Seriously though, I think it is taught as a standard collocation in British-published course books, especially those for Business English. Which is a little strange, as even in BrE, "make a decision" is more common. I think I might belong to the "take" school, but I don't know why (perhaps it's because I'm an EFL teacher and have picked it up from there).

There's another point - in some languages, like French and Spanish, the standard verb is "take" - prendre une décision, tomar una decisión.

Wouldn't the easiest thing be to look in a dictionary?

Yup. Demonstrative pronouns (and determiners - "that book you're reading") can't be omitted.