I love the Question Rule! I run through a gradual derivation of it with my education students so they can see how tricky it is to teach people with language delays and people learning English as a foreign language. Most people (however automatically they form grammatical sentences) have no idea how they do it!
The basic rule is purely formal (as opposed to semantic): when there’s an auxiliary or “be”, use that; otherwise use “do”.
Is that unusual?
Are you noticing anything unusual?
Have you noticed anything usual?
Had you noticed anything unusual at that point?
Will you report anything unusual?
Might you have noticed something unusual?
“Do”, like the fronted auxiliary verbs in the above sentences, is what carries the tense:
Did/do you see anything unusual?
And here’s Doug:
That would be what at least John McWhorter1refers to as the “meaningless do”, which is one of the features of English that makes it an odd language. His claim (or perhaps speculation?) is that it came into the language by contact with Celtic languages. And you’re right, it can be very hard for ESL students to learn idiomatically.
In most Germanic languages, a pattern like, “Eat we breakfast?” would be idiomatic, where in English the idiom, of course, is “Do we eat breakfast?”
1. Linguistics Prof at Columbia and brilliant lecturer on linguistics, including in the Great Courses series↩