So I found out about the philosophic term counterfactual, which can essentially function as a synonym for the what_if tag because it covers images of situations or paradoxes that go against facts in the story. Counterfactual logic normally is applied to hypothesizing how historical events could have been different if something else happened, such as:

"If Lee Harvey Oswald didn't shoot President Kennedy, someone else would have."
OR, "If Lee Harvey Oswald didn't shoot President Kennedy, the President would have survived."
OR, "If Lee Harvey Oswald missed his shots, the President would have survived."
OR, "If Lee Harvey Oswald missed his shots, someone else would have died."

And so on...

But the images in the what_if tag are conveying the same principle, such as:

• "If Shizuki Hitomi became a magical girl, this is what her costume and weapon would look like." (post #844743, post #882211, post #949024, etc.)
• "If Gilgamesh was Waver Velvet's servant instead of Toosaka Tokiomi's, the dynamics between them would have been strained at best." (post #1079899)
• "If Alisha was a Seraph instead of a Human, she would be able to perform Kamui with Sorey or Rose." (post #1931980)

Just a short list of existing examples, although most I saw had to do with playing around with the Master/Servant relationship in the Fate series, or making ordinary females in the Precure series as Cures when this never happens, or some spoilery ones for Kill la Kill.

My question is whether or not a what_if <-> counterfactual alias should be made, or if things should be left as is. I understand if 'counterfactual' isn't exactly an everyday word to use for hypothetical situations, as saying 'what if...' or 'if this happened...' are much easier for taggers to remember. The biggest difference between the two that I see is "what if" = phrase VS "counterfactual" = noun, and we tend to use nouns instead of phrases as tags on this site unless it's a meme or a copyright.

And no, I don't want to apply this to if_they_mated because at least some images depict matings that could be entirely possible in the context of the story, but just not shown officially. If it's known to be totally impossible in the story, then this could be added manually.

You found a term that has the same meaning, but replacing the simpler term with the more complex in this situation might be superfluous. If both mean the same thing, and we've done fine without the new term, it isn't really useful to do a change if the understanding they both do the same thing is there. Unless the new term prevents tagging errors with its existence(something a longer word won't do), or streamlines things(I doubt this too), then we should keep the old term. If there is a wiki for what_if, maybe slipping in the term as a descriptor would refine people's understanding of the concept, regardless of the words used. Otherwise, aliasing is to me unnecessary in either direction.