Stan Carey writes on his blog that "'Because' has become a preposition". Here's an example he gives:
No work tomorrow because holidays!
The reason for calling this a "prepositional because" seems to be the assumption that this is short for
No work tomorrow because [of] holidays!
The idea seems to be that the elided preposition "of" has been absorbed into the "because", which is now a new kind of preposition. But that's not what I think the sentence is short for. I think it is short for
No work tomorrow because holidays [are here]!
In other words, of the two conventional ways "because" can be used, I submit that it is being followed by a finite clause ("holidays are here") and not a prepositional phrase ("of holidays"), and it is the finite clause that has been shortened to just "holidays".
This is not a new thing. We do it all the time. Carey says he hesitates to call this ellipsis, but that is exactly what it is. It turns out[*] there is something called answer ellipsis where we answer questions with short fragments rather than complete sentences. Here's an example from Wikipedia, slightly modified:
Q: Why will they resist our help? A: Pride.
"Pride" isn't a complete sentence — it's just a noun — yet it counts as an elliptically grammatical answer to the question. The listener understands it to mean "They will resist our help because they have pride." Likewise:
Q: Why is there no work tomorrow? A: Holidays!
So when we say
No work tomorrow because holidays!
the "because" is still a subordinating conjunction, but we are allowing it to be followed by a third thing — not just
(1) a finite clause
or
(2) a prepositional phrase
but also
(3) an answer ellipsis
This theory fits the facts better than the "prepositional because" theory, because as Carey points out, the "because" doesn't have to be followed by a noun. He quotes examples from Twitter where it is followed by a verb:
Bye going to study for English because didn't finish this morning because fell asleep
Hot cocoa because need.
And examples where "because" is followed by an adjective:
Going to bed way early because exhausted:/
{Falls on her bed and cuddles pillows because tired}
A preposition is never followed by a verb or an adjective, so it doesn't make sense to call these examples of "prepositional because". On the other hand, they do fit the answer ellipsis model:
- Q: Why didn't you finish studying English? A: Fell asleep!
- Q: Why are you getting hot chocolate? A: Need! (As in "I need it!")
- Q: Why are you going to bed early? A: Exhausted!
- Q: Why did you fall on your bed? A: Tired!
A number of commenters on Carey's blog post agree with me that "because" is still a conjunction, but I haven't seen anyone else call the part after "because" an answer ellipsis.
[*] "It turns out" is shorthand for "I didn't know this until I looked it up today."