Englishfor English speakers
unless
Preposition
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If you say that mathx/math is true unless mathy/math, mathx/math is true only if mathy/math does not happen or is not true.
I'll be there at 8:30 unless the train is late.
Unless you help, we won't finish on time.
otherwise
Adverb
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You use otherwise to connect two clauses where the second clause shows the bad thing that would happen if the first clause doesn't happen.
You need the proper license. Otherwise you can't do business.
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You use otherwise to connect two clauses where the second clause shows what would have happened if the first clause hadn't happened.
I missed the bus. Otherwise, I would have been here earlier.
—
If you think or say otherwise, you don't agree.
She says we should put him in piano lessons, but I think otherwise.
—
apart from something else
She has some cuts, but is otherwise fine.
He just had to wash the dishes. Otherwise, everything was done.