If (someone) were to become vs. if (someone) became… + COULD

Question

Let's say there is a married couple, Sandra and Jake. Sandra wanted to go to her ailing mother, whereas, Jake wanted to go on a holiday next week. If they didn't go to her mother:

if Sandra's mother were to become seriously ill, Sandra could not forgive here husband.

To

if Sandra's mother became seriously ill, Sandra could not forgive here husband.

This is a 2nd conditional modal verbs usage, and I know how to construct #2 sentence. But why is that were to become was used instead of the other?

If an ESL would like to use both of them, are they grammatical to use?

P.S.: There is a correct answer below, but, I have just edited this to clarify what I am really trying to ask.

Answer 1

Both sentences are grammatically correct. The second sentence uses a backshift to indicate that we are talking about a hypothetical situation- this is used for all verbs except be. The first one uses a proper subjunctive were (the only one!).

The first (with were) is, in my opinion, stronger in suggesting a hypothetical situation. In this situation- Sandra's mother is probably no spring chicken and already 'ailing'- we are probably talking about something that could really happen, so the less strongly hypothetical version became is more appropriate.

The were version is slightly more formal than the became version, but both are a lot more formal, and less widely used, than one using got if you make the second part less formal too, you get:

If Sandra's mother [got] seriously ill, Sandra [would never] forgive here husband.

This NGram graph shows the trend toward the less formal (got) usage: remember that Google Ngrams is based mainly on written English, and for informal usage it lags a long way behind spoken English.

Answer 2

The if -- were form is called the subjunctive mood or just subjunctive. It is used in a hypothetical situation, contrary to fact.

An example would be the lyrics for If I Were a Rich Man, by Harnick and Bock.

If I were a wealthy man...

If I were rich, I'd have the time that I lack...

Poor Tevye doesn't have two kopeks to rub together in his pocket, so being rich is contrary to fact.

Answer 3

The two sentences are constructed differently, but they are both valid expressions of conditional II. See the Wikipedia summary:

If the condition clause uses the past tense of another verb, it may be replaced by the auxiliary construction were to + infinitive (particularly if it has hypothetical future reference).

There's no functional difference between the two, except that "were to" sounds more formal to most speakers; in casual conversation, you would be more likely to use sentence #2.