How do I correctly determine realis vs irrealis or indicative vs subjunctive in this sentence?

I stared at him to see if he were just a cartoon character.

or

I stared at him to see if he was just a cartoon character.

The intended meaning of the two sentences above are that due to him (his behavior) that the writer is (I am) staring at, that is, in the writer's imagination, they are imagining because of his absurd statements prior, that he is cartoonish. The writer is being sarcastic, because they know that he is not actually an animated cartoon, but rather he is just acting like one.

I'm confused about whether it should be was or were, however (I'm a native English speaker) my intuition tells me it should be was and another person is telling me that it should be the subjunctive were.

Any help gladly welcomed!

Answer

I stared at him to see if he was just a cartoon character.

The sentence above has a clause which looks like a conditional adjunct:

• if he was just a cartoon character

If this was indeed a conditional antecedent, then we could use either was or were here, assuming that the conditional was a so-called subjunctive conditional.

However, the if-string above is not part of a conditional construction in the Original Poster's sentence. It is an interrogative clause. We can apply a simple test here, which is to replace the word if with the interrogative subordinator whether. If the sentence is still grammatical and means the same thing, then we know that this is an interrogative clause and not a conditional adjunct:

I stared at him to see whether he was just a cartoon character.

The sentence above means the same thing as the Original Poster's example sentence, so we can be confident that the string involved is an interrogative clause. Because this is a straightforward interrogative clause, there is no possibility of using irrealis were here.