The key to understanding when to use was or were in a sentence is determining whether you need to use the subjunctive mood or not. A verb is in the subjunctive mood if it expresses an action or state that is not reality. For example, it might be hypothetical, wished for, or conditional.
“Was” and “Were” as Past and Subjunctive Verb Tenses
To better see what we are up against when deciding when to use was or were, let’s compare the past and subjunctive conjugations of to be side by side.
Our chart reveals something delightful. You can’t go wrong choosing were with the second person (you), the first person plural (we), the second person plural (you), or the third person plural (they). We only need to make a choice about when to use was or were with the first person singular (I) and the third person singular (he, she, or it). Isn’t that great news?
Is It “If I Was” or “If I Were”?
Use were if the state of being you are describing is in no way the current reality. This is true whenever a hypothetical situation is expressed, for example.
Would you invite me over if I were more polite at the dinner table?
The first sentence can be described as an unreal conditional clause. These hypotheticals are easy to spot because they are often introduced by an if and are related to another clause containing a would or could.
Another type of unreal conditional sentence that uses the same construction demanding the subjunctive were is the impossible or improbable type.
Here the speaker implies that the puzzle is unsolvable. Therefore, solving the puzzle is not a likely reality, and the subjunctive were is used instead of the past tense was.
That does not mean that every clause beginning with if I requires the use of if I was rather than if I were.
In this sentence, the speaker acknowledges that it is possible he or she may have incorrectly thought that Felicity loves puppies and has given her a puppy in error. The fact that it is possible the speaker is describing reality makes this an indicative sentence, not a subjunctive one. Therefore, we use was instead of were.
Use “Were,” Not “Was,” for Wishful Thinking
A sure sign that you should use the subjunctive is when the word wish is used. A wish is the desire or hope for something that cannot or probably will not happen.
He wishes his grammar were better.
I wish the stories about me were true, but I am not really the master of the universe.
She wishes she were at least five inches taller.
Always remember this rule about the usage of was and were: use were with expressions that are hypothetical, wishful, imagined, desired, doubtful, and otherwise contrary to fact—that is to say, not real.