In American English, what part(s) of speech are "or else" and "otherwise" and why is "otherwise" more flexible if it's the same part of speech?
Take the following examples:
1a. Clean your room, or else I will ground you.
1b. Clean your room, otherwise I will ground you.
2a. Clean your room; I will ground you or else.
2b. Clean your room; I will ground you otherwise.
Sentences 1a and 1b have identical meanings and are both grammatically valid. (I'm not worried about the minor issue that perhaps, stylistically, 1a could definitely go without the comma, whereas 1b might feel wrong without the comma.)
However, while 2b is grammatically valid and has the same meaning as 1b, meanwhile 2a is grammatically invalid without a comma before "or." (We can't put a comma before "or" without changing the meaning of the sentence. "I will ground you, or else," threatens me with punishment if I fail to punish you. That is a very different statement than 1a, which threatens you.) See the definition of "or else".
So, again, my question is, which part(s) of speech are "or else" and "otherwise" in this context? If they're the same part of speech then why does the grammar and meaning change for "or else" but not for "otherwise" in sentence group 2?
Best Answer
Traditionally, 1b requires a semicolon or full stop:
The reason is that otherwise is traditionally considered an adverb, and two sentences can traditionally only be joined with a mere comma if there is a conjunction between them:
This is traditionally considered a "comma splice", which is undesirable in formal English. Consequently is an adverb and not a conjunction.
Here the conjunction and makes the comma possible.
Or is a conjunction, so no problem there.
Or else is two words, and hence two parts of speech, not one. The problem here is that else is traditionally considered an adverb, and so it has to be part of the sentence that it modifies; in other words, it tells the reader that the threat I will ground you is the "other" ("else") possibility, and so it should be part of that clause. If you put else after or, it becomes part of the clause that starts after or; after all, or is a conjunction here, and it begins a new clause.
Informally, you can end a sentence with or else, but that is elliptical, and the "other" possibility (the threat) is omitted:
In your example, the threat is explicitly mentioned, so else needs to be in the same clause as the content of the threat.