what is the main clause in conditional sentences

Question

I have a compound sentence followed by an if clause, how do I know what the if clause is referring to?

Sam will become a husband and a stepfather if he will marry Jane.

My understanding is that the subject (Sam) and verb (become) extends to “husband” and “stepfather”. So that “Sam will be a husband and Sam will be a stepfather = Sam will be a husband and stepfather.”

If this is true, does the “if” clause refer to Sam becoming both a husband and a stepfather or does the “if” clause only refer to Sam becoming a stepfather? And why?

Answer 1

Sam will become a husband and a stepfather if he will marry Jane.

The title of your question is 'What is the main clause ...' The answer is that it's the whole sentence. The conditional element, irrespective of interpretation, is an adjunct embedded within the main (matrix) clause .

That aside, the more salient interpretation is that Sam will become both a husband and a stepfather if he marries Jane. The potential for ambiguity is so minimal that it can be discounted.

Answer 2

This is generally a matter of context; here, as the realizations of the notion of becoming a husband and that of becoming a stepfather are indubitably incidental to one another -- provided Jane has already a child or is about to have one, and the context does imply that --, necessarily, the "if" clause does refer to both. However, you could have chosen a different example, as for instance the one shown next.

• Sam will become a mathematician and a musician if he makes progress fast enough with his guitar training.

There is certainly some imprecision in this situation: is it the case that if the guitar training takes too much time the guitar studies will be abandonned, the normal plan taking its course and Sam becoming a mathematician, or is it the other way? One would tend to believe that it is not the other way but there is no certitude of this eventuality being correct.

This is resolved by using a comma after "mathematician".

• Sam will become a mathematician, and a musician if he makes progress fast enough with his guitar training.

In spoken English the comma could eventually be rendered by an abnormally long pause, the remainder of the sentence being then added as an afterthought, and then there could be no ambiguity.

It is, otherwise, always possible to make modifications in such sentences so as to give them a clear interpretation.

• Sam will become a mathematician in any case, and a musician if he makes progress fast enough with his guitar training.

• Sam will become a mathematician and if he makes progress fast enough with his guitar training also a musician.