Adverb clauses are adverb clauses whether they come at the beginning of a sentence or at the end.
If I could go with you, it would be nicer.
It would be nicer if i could go with you.
Let's try to identify "it." That's the subject.
The trip would be nicer if I could go with you.
If I could go with you, the trip would be nicer.
Many of us use "it" too much. I'll often go back into my writing and substitute what I actually mean for the "it." IT makes the writing more clear.
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