Yes/no questions are formed by moving the first auxiliary verb to the beginning of the sentence, before the subject. In sentences without an auxiliary verb, a form of 'do' is added to the beginning. For example, 'You are ready' becomes 'Are you ready?' and 'She likes pizza' becomes 'Does she like pizza?'
Start with sentences that already have an auxiliary (is, are, was, were, have, has) and practice moving them to the front. Then introduce sentences without auxiliaries and show how to add 'do', 'does', or 'did'. Have students compare statement and question pairs side by side.
Students may invert the subject and main verb without moving the auxiliary. They might forget to add 'do/does/did' in simple present and past. Some learners think all verbs can just move to the front without an auxiliary.
You've learned that every English sentence has a subject and a predicate, and that auxiliary verbs like *is*, *are*, *was*, *were*, *have*, *has*, *can*, *will*, and *should* attach to main verbs to add meaning about time, possibility, and aspect. Those two pieces of knowledge are exactly what question formation operates on. The grammatical operation for forming yes/no questions in English is subject-auxiliary inversion: move the first auxiliary verb to the position before the subject, and the sentence becomes a question.
The operation is straightforward when a sentence already contains an auxiliary: "You are ready" → "Are you ready?" "She has finished" → "Has she finished?" "They can leave" → "Can they leave?" Notice that the main verb doesn't move — only the first auxiliary does. In "She has been working," the first auxiliary is *has*, so the question is "Has she been working?" — not "Been she has working?" The rule is anchored to the auxiliary, not the main verb, because auxiliaries are the grammatical carriers of tense and modality, not the verb that carries the main meaning.
The complication arises in the simple present and simple past, where English declarative sentences have no auxiliary at all. "She likes pizza." "He worked late." There is nothing to invert. English solves this with a process called do-support: insert a form of *do* to serve as a placeholder auxiliary, carry the tense on that auxiliary instead of the main verb, and then invert the do into question position. "She likes pizza" → "Does she like pizza?" (Note: the -s moves from *likes* to *does* — the main verb reverts to its base form.) "He worked late" → "Did he work late?" (The past tense moves from *worked* to *did* — again, the main verb loses its inflection.) Do-support reveals that English question formation fundamentally requires an auxiliary, and if none exists, the grammar creates one.
The do-support rule has a neat implication: when a sentence already has an auxiliary, *do* is never inserted. "She is going" does not become "Does she is going?" — it becomes "Is she going?" The auxiliary already present handles the inversion. Do-support is a last resort, deployed only in its absence. This is why "be" and "have" (as main verbs in some dialects) pattern differently: "Are you tired?" not "Do you be tired?"
The deeper insight from studying question formation is that English word order is not a surface convention — it encodes grammatical structure. The declarative order (subject before verb) and the interrogative order (auxiliary before subject) are both rule-governed, and the rules interact systematically with everything you know about subjects, predicates, and auxiliaries. Mastering inversion means you can form questions in any tense, any mood, with any auxiliary — not by memorizing individual question templates, but by applying a single operation to your existing grammatical knowledge.