This sentence is a 2nd Conditional sentence.
Conditional 2 sentences are used to describe hypothetical situations.

Examples:

If John were a dog, he would be a Labrador.

If John owned a dog, it would be a Labrador.

The two main characteristics of Conditional 2 sentences are:

1. They deal with hypothetical present situations with conditions that are unlikely or even impossible to be met.
2. The result is unrealistic or impossible.

We should always use "WERE" instead of "WAS" in the condition clause because that's simply what the rules say.

GaneshMalkar wrote:Rossy would feel better if she was my daughter.

Why "was" is wrong here and we should be using "were"?

I understood that "would" is in conditional hypothetical subjunctive mood and with this mood, we should use past tense verb which is appropriately used here "was"....Why "was" is wrong here?

Hi Ganesh,

The reason is grammar. When we have to use a subjunctive tense, it should always be 'were'. Subjunctive means that you are Wishing for something.

In your example, Rossy is not his daughter and he is trying to express a wish so its subjunctive. Hence 'Were' and not 'Was'.

In gmat ignore what might sound colloquially correct

Hope this helps.

Regards,
Pritish

Kasia@EconomistGMAT wrote:This sentence is a 2nd Conditional sentence.
Conditional 2 sentences are used to describe hypothetical situations.

Examples:

If John were a dog, he would be a Labrador.

If John owned a dog, it would be a Labrador.

The two main characteristics of Conditional 2 sentences are:

1. They deal with hypothetical present situations with conditions that are unlikely or even impossible to be met.
2. The result is unrealistic or impossible.

We should always use "WERE" instead of "WAS" in the condition clause because that's simply what the rules say.

Correct me if I'm wrong :-

1.If<simple past>,Then<Simple past>
the above statement talks about a fact,which is not valid today.Also,the simple past can be singular.

2.If<subjunctive verb (always plural)>,Then<would/could>
This statement is being made in present time about something uncertain.Also,the subjunctive verb is always plural