Unless the earth had a moon, there wouldn’t be any tides.
I am confused with the use of ‘unless’ in this sentence.
The sentence is taken from a test question. Please explain it to me.
It is a strange one, as you can understand the meaning, but would be better written as “If the Earth did not have a moon, there wouldn’t be any tides.” The word unless tends to be used to describe a sentence structured as:
“Unless X is true, Y will not be true.”
“Y will not happen unless X happens.”
In your example, you could restructure the sentence to say:
“There wouldn’t be any tides unless the Earth had a moon.”
However, this will not usually be considered correct because the word “unless” is not generally used to speak of known facts. The Earth does have a moon, so it would not make much sense to say that “something won’t happen unless the Earth has one”. It makes more sense to say in this instance:
“There would be no tides if the Earth had no moon.”
This could also be structured more similarly to your example:
“If the Earth had no moon, there would be no tides.”