# "I do X if Y, and Z otherwise" vs. "I do X if Y, or Z otherwise"

Which one(s) amongst the following sentences are correct, and which one sounds the best?

• "I do X if Y, and Z otherwise"
• "I do X if Y, or Z otherwise"
• How formal is this statement supposed to be? Is this statement meant to be part of a contract, law, or regulation? Or part of a computer program? Or part of an essay? Or just an off-hand comment to a friend? Oct 26 '15 at 2:12
• @Jasper research article Oct 26 '15 at 2:13

To answer your question directly and literally as written, I suggest the second sentence sounds the best.

I do X if Y, or Z otherwise.

My reasoning is more based in logic than grammar. The choices are an "either/or" proposition (i.e., mutually exclusive) and not a "both/and" proposition.

Source: Native speaker

• One infallible source I'd say. :P Oct 26 '15 at 19:02

"Otherwise" is a conjunctive adverb, so an additional coordinating conjunction ("and", "or") is not needed. Replace the coordinating conjunction with a semicolon.

If X, I do Y; otherwise, I do Z.

You can also use two separate sentences.

If X, I do Y. Otherwise, I do Z.

• Why a semicolon and not a comma? Oct 26 '15 at 17:10
• A comma can be used with coordinating conjunctions (e.g. "and", "but", "or"), but not with conjunctive adverbs. As a rule, an adverb cannot join sentences.
– woz
Oct 26 '15 at 20:48
• Is that so? en.wikipedia.org/wiki/Conjunctive_adverb (see "Placement") doesn't even mention a semicolon... Oct 26 '15 at 21:07
• You don't have to use a semi colon, but you cannot use only a comma. Another valid option is two separate sentences. A semicolon is a good choice for two closely related sentences though.
– woz
Oct 26 '15 at 21:48