The small verb that controls the whole sentence
A school report includes a simple question: ‘Did the team measured the water level?’ The student notices that measured looks correct in a sentence about the past. But the auxiliary did has already carried the past-tense information. The main verb must be measure. A single repeated tense marker makes the question ungrammatical, even though its meaning remains easy to guess. That is the sort of error a competent editor learns to recognise before the paper begins.
This guide deals with auxiliary verbs: the small grammatical helpers that carry tense, form questions and negatives, combine with participles, and let a writer answer without repeating an entire predicate. The central task is not to collect a long list of ‘right expressions’. It is to see the structure of a clause and identify which verb is responsible for which grammatical job. If we can locate the auxiliary, its subject and the following verb form, most of the difficult-looking examples become ordinary decisions.
The immediate predecessor is Volume 0293 on verb complements. This new volume takes a different role: auxiliary agreement, auxiliary order and the base form or participle that each helper licenses. Earlier lessons remain owners of their own intents. Use Volume 0106 for general subject–verb agreement, Volume 0169 for what modal choices mean, and Volume 0173 for active/passive agency. Here we use those foundations only where an auxiliary decision needs them.
The official 2027 G3 English examination
The first Singapore–Cambridge Secondary Education Certificate examination takes place in 2027. The official 2027 G3 syllabus directory, updated 26 October 2026, lists English Language as K300, with 1184 as the 2026-and-earlier O-Level reference code. In the official K300 syllabus, Paper 1 Writing lasts 1 hour 50 minutes, carries 70 marks and accounts for 35% of the English assessment. Section A Editing contributes 10 marks. Candidates correct grammatical errors in a continuous text of no more than 250 words. This section does not test spelling or punctuation errors.
Paper 1 also contains Situational Writing for 30 marks and Continuous Writing for 30 marks. Paper 2 Comprehension carries 50 marks and 35% of the assessment; the Listening and Oral Communication papers carry 10% and 20% respectively. Our practice concerns grammatical editing and transferable control of sentences, not a claim that every example is an official question or that knowing auxiliaries alone prepares a candidate for every paper. In an actual examination, read the instructions and the whole passage before changing a word.
Four auxiliary jobs
First, be helps form continuous verb phrases: ‘The team is measuring the container.’ It also helps form passives: ‘The container was measured.’ Second, have helps form perfect phrases: ‘They have measured it.’ Third, the modal auxiliaries—such as can, could, may, might, must, should, will and would—typically precede a plain verb form: ‘They should check.’ Fourth, do, does and did support many questions, negatives and emphatic statements when no other suitable auxiliary is present.
The useful question is: what is the first auxiliary doing, and what shape must the following verb take? In ‘Did she check?’, did carries past tense and check stays in its base form. In ‘She has checked’, has takes a past participle. In ‘She is checking’, is takes an -ing form. In ‘It has been checked’, has and been form a chain ending in a past participle. These are patterns to understand, not words to swap mechanically.
Why a grammatical correction must preserve meaning
An editing answer may look neat but change what a statement says. ‘The sample has been checked’ indicates a completed check with a connection to the present. ‘The sample is being checked’ describes an ongoing check. Both are grammatical, but they are not interchangeable. Similarly, changing ‘could have failed’ to ‘must have failed’ changes the writer’s degree of certainty; that is not a harmless grammatical repair. The editor should keep the original time relationship, agency, certainty and polarity unless grammar makes a change necessary.
Read the clause before and after an apparent mistake. If the report says the team checked the figures yesterday, a past-time question may need did and a base-form verb. If the question instead concerns a completed action relevant now, has plus a past participle may be appropriate. Do not impose a favourite pattern on every context. The difference between correcting a form and rewriting an assertion is one of the most important habits an advanced learner can acquire.
A compact diagnostic for the editing passage
Read the full text once for who did what and when. On the second pass, underline the finite verb or the first auxiliary of a suspicious clause. Ask whether the subject agrees with it, whether a direct question needs inversion, whether do-support is required, and whether the following verb has the correct base, -ing or past-participle form. Finally reread the corrected sentence in context. If it makes a different claim, reconsider before recording the correction.
Do not insert an auxiliary merely because a sentence looks short. ‘What the team recorded remains unclear’ is a complete sentence containing an embedded clause, while ‘What did the team record?’ is a direct question. ‘The results were collected and checked’ shares one auxiliary legitimately. An editor who adds were before checked has not necessarily repaired an error. It is often just a less concise version of a correct sentence.
Thirty-six worked decisions in meaningful context
All sentences below are original teaching examples. They are not reproduced from examination papers. Some contain grammatical errors; others are correct and are deliberately included because unnecessary edits can damage meaning. For each, decide whether correction is necessary, identify the auxiliary structure, and then explain why the result says the same thing as the intended original. Work on the sentence before reading the answer, then compare its grammatical job with the next case.
Decision 01 — Present simple with a singular subject
Read the sentence. The notice says, ‘The caretaker do not approve unsupervised access.’ Decision. Change do to does: ‘The caretaker does not approve unsupervised access.’
Why. A third-person singular subject takes does in a present-simple negative. The main verb stays in the base form approve. Transfer test. Try the plural subject caretakers. Which helper changes, and which main verb remains the same?
Decision 02 — Present simple with a plural subject
Read the sentence. The draft reads, ‘The monitors doesn’t record the time.’ Decision. Change doesn’t to don’t: ‘The monitors don’t record the time.’
Why. The plural subject monitors requires do, not does. The contracted negative does not alter that agreement. Transfer test. Replace the subject with one monitor and repeat the decision.
Decision 03 — A past negative
Read the sentence. The report states, ‘The group did not measured the water level.’ Decision. Change measured to measure: ‘The group did not measure the water level.’
Why. The auxiliary did already marks the past. Putting past tense on the following lexical verb repeats the same grammatical marking. Transfer test. Keep the negative but change the subject to two groups. Does the main verb form change?
Decision 04 — Past-time question
Read the sentence. A student asks, ‘Did the team calculated the capacity?’ Decision. The correct question is ‘Did the team calculate the capacity?’
Why. After did, the ordinary lexical verb appears in the base form, even when the event happened yesterday. Do not change the event’s time to repair the sentence. Transfer test. Now make the same question negative without replacing the past-time meaning.
Decision 05 — Present question about a singular report
Read the sentence. A heading reads, ‘Does the report explains the units?’ Decision. Use ‘Does the report explain the units?’
Why. The auxiliary does carries the present-tense third-person-singular marking. The lexical verb stays explain, not explains. Transfer test. Compare the statement ‘The report explains the units.’ Where has the -s marking gone?
Decision 06 — Present question about a plural set
Read the sentence. A questionnaire asks, ‘Does the charts show similar trends?’ Decision. Use ‘Do the charts show similar trends?’
Why. The plural subject charts requires do. The main verb stays in the base form after either do or does. Transfer test. Replace charts with chart; repair both parts if necessary.
Decision 07 — An ordinary affirmative statement
Read the sentence. The notice says, ‘The staff do checks each morning.’ Decision. In ordinary affirmative prose, write ‘The staff check each morning’ if staff means multiple staff members and check is the intended action.
Why. Do is not normally inserted before the lexical verb just to mark present tense. Emphatic do is possible when there is an actual contrast, but this sentence offers none. Transfer test. Imagine a false accusation that staff never check. How would emphatic do now change the tone?
Decision 08 — Do-support with an emphatic correction
Read the sentence. A writer says, ‘The team did check the seals, despite the rumour.’ Decision. No grammatical correction is needed. The emphatic did highlights that checking really happened.
Why. A learner who changes did check to checked may remove a meaningful contrast, even though the shorter sentence remains grammatical. Transfer test. When would an emphatic auxiliary be appropriate in an examination report, and when would it sound defensive?
Decision 09 — A direct question’s order
Read the sentence. A student writes, ‘Where the scientists have stored the samples?’ Decision. Write ‘Where have the scientists stored the samples?’
Why. In an ordinary direct question formed with the perfect, the auxiliary have precedes the subject. Do not invent did when have is already available. Transfer test. Turn the question into a statement beginning ‘The supervisor asked where…’ and check the word order.
Decision 10 — An embedded question’s order
Read the sentence. A report says, ‘We need to know where have the students stored the samples.’ Decision. Use ‘We need to know where the students have stored the samples.’
Why. The words beginning where form an embedded question, not a direct question. The ordinary subject–auxiliary order returns inside that embedded clause. Transfer test. Compare ‘Where have the students stored the samples?’ What changes when the sentence becomes indirect?
Decision 11 — Question words are not always followed by do
Read the sentence. A teacher asks, ‘Who did checked the record?’ Decision. Use ‘Who checked the record?’ when who asks for the subject of the past-time action.
Why. A subject question can place the interrogative word directly in the subject position without do-support. ‘Who did check?’ can exist as an emphatic question in special contexts; do not automatically use it for a neutral inquiry. Transfer test. Compare ‘Who checked the record?’ with ‘What did the team check?’ Which question word is the subject?
Decision 12 — Modal followed by a base form
Read the sentence. The instruction reads, ‘Students must to submit the reading.’ Decision. Use ‘Students must submit the reading.’
Why. The modal must is followed by a bare infinitive, not to plus infinitive. The mistake is the extra to, not the intended obligation. Transfer test. Rewrite with ‘have to’ instead of ‘must’. What form follows to?
Decision 13 — Modal plus wrongly inflected main verb
Read the sentence. The notice says, ‘A learner can understands the formula.’ Decision. Use ‘A learner can understand the formula.’
Why. A modal such as can takes the base form after it, regardless of the subject’s singular number. Understands belongs to a simple present clause without that modal. Transfer test. Replace can with could and explain why the main verb stays unchanged.
Decision 14 — Two ordinary modals cannot simply be stacked
Read the sentence. The draft promises, ‘The visitors will can inspect the display.’ Decision. If the intended meaning is future ability, write ‘The visitors will be able to inspect the display.’
Why. Standard English does not ordinarily combine will can into one modal chain. The phrase be able to expresses the required ability after will. Transfer test. How would the statement change if the inspection were merely a possibility rather than a planned permission?
Decision 15 — An -ing form after be
Read the sentence. The observation says, ‘The staff are measure the depth now.’ Decision. Use ‘The staff are measuring the depth now.’
Why. Continuous aspect is formed with an appropriate form of be followed by the present participle. The time marker now supports an ongoing action. Transfer test. Change the sentence to a completed event yesterday. Which auxiliary structure would you no longer need?
Decision 16 — A singular subject in a continuous clause
Read the sentence. The observation says, ‘The monitor are recording the time.’ Decision. Use ‘The monitor is recording the time.’
Why. The auxiliary be must agree with the singular subject monitor; the -ing form recording remains unchanged. Transfer test. Use the subject ‘The monitors’. Which word changes in the auxiliary phrase?
Decision 17 — Perfect aspect and a past participle
Read the sentence. The statement reads, ‘The learners have chose an option.’ Decision. Use ‘The learners have chosen an option.’
Why. Perfect aspect takes have plus a past participle. For choose, the past participle is chosen, not the simple past chose. Transfer test. Compare ‘The learners chose’ and ‘The learners have chosen’. What time relationship might distinguish them?
Decision 18 — Perfect aspect with a singular subject
Read the sentence. The report says, ‘The team leader have checked the costs.’ Decision. Use ‘The team leader has checked the costs.’
Why. The subject is the singular team leader, so the present-perfect auxiliary is has. The participle checked remains as it is. Transfer test. If the writer says ‘The team leaders’, does the verb phrase require one change or two?
Decision 19 — A mixed chain of have and be
Read the sentence. A notice reads, ‘The samples have being labelled.’ Decision. Use ‘The samples have been labelled.’
Why. The perfect passive uses have been followed by a past participle. Being cannot replace been in this short chain without another auxiliary and a different aspect. Transfer test. Compare the ongoing passive ‘The samples are being labelled.’ Which grammatical job changes?
Decision 20 — Present perfect continuous
Read the sentence. The report says, ‘The students have been work on the model.’ Decision. Use ‘The students have been working on the model.’
Why. The perfect continuous uses have been plus the -ing form. The chain combines a relationship to the present with activity extended over time. Transfer test. Could the sentence instead say ‘The students have worked’? Explain the possible difference without calling either form universally wrong.
Decision 21 — A simple passive
Read the sentence. A draft reads, ‘The volume was calculate from the measurements.’ Decision. Use ‘The volume was calculated from the measurements.’
Why. The passive requires be plus a past participle. The past tense is carried by was; the final verb form is a participle, not a base form. Transfer test. Change the sentence into the active voice with an explicit actor. Which information becomes more visible?
Decision 22 — A progressive passive
Read the sentence. A notice says, ‘The container is been inspected.’ Decision. Use ‘The container is being inspected’ for an inspection happening now.
Why. The present progressive passive has is being plus a past participle. ‘Has been inspected’ would express a completed inspection and may not preserve the writer’s intended time. Transfer test. If the notice concerns a completed inspection with present relevance, which chain would be more suitable?
Decision 23 — A past perfect passive
Read the sentence. The report states, ‘The sample had been label before the meeting.’ Decision. Use ‘The sample had been labelled before the meeting.’
Why. The sequence had been requires a past participle. The earlier-time meaning remains: labelling took place before another past event. Transfer test. Would ‘was labelled before the meeting’ necessarily be ungrammatical? Explain the difference between a possible alternative and a required correction.
Decision 24 — Auxiliary agreement in a passive
Read the sentence. A draft says, ‘The results has been reviewed.’ Decision. Use ‘The results have been reviewed.’
Why. The plural noun results controls have. A passive participle does not cancel subject–auxiliary agreement. Transfer test. Replace ‘results’ with ‘report’. How does the first auxiliary change?
Decision 25 — An already correct shared auxiliary
Read the sentence. The note states, ‘The report was drafted and checked by two teachers.’ Decision. No correction is needed. One auxiliary was legitimately serves both past participles, drafted and checked.
Why. Not every absent repeated helper is an error. The two actions share the same passive subject, time and structure, making the sentence grammatical. Transfer test. Would adding a second ‘was’ necessarily make the sentence wrong? Or merely longer?
Decision 26 — A shared auxiliary with mismatched forms
Read the sentence. A draft says, ‘The measurements were recorded and comparing with the plan.’ Decision. Use ‘The measurements were recorded and compared with the plan’ if both completed actions are intended as passives.
Why. The shared auxiliary were requires compatible participle forms for the coordinated actions. The -ing word breaks the intended shared passive construction. Transfer test. Try rewriting the sentence so that one action is ongoing and the other is completed. Can you still share only one auxiliary?
Decision 27 — An auxiliary in a short affirmative reply
Read the sentence. A student asks, ‘Has the diagram been revised?’ Another replies, ‘Yes, it has.’ Decision. The reply is grammatical. Has stands in for the recoverable perfect predicate; repeating ‘been revised’ is optional.
Why. Short responses often use the same auxiliary family as the question. Adding a new tense or a different helper may change the answer’s relationship to time. Transfer test. Compare ‘Yes, it is’ and ‘Yes, it has’. Which question would each answer naturally follow?
Decision 28 — A short negative answer
Read the sentence. To ‘Did you check the figures?’, a learner answers, ‘No, I didn’t.’ Decision. The reply is grammatical and uses the past-time auxiliary of the question. The omitted main verb remains understood.
Why. The sentence is not a fragment merely because it omits ‘check the figures’. Its auxiliary supplies enough structure to recover the meaning. Transfer test. Would ‘No, I don’t’ normally answer the same yesterday-specific question? Explain why it might refer instead to a habit.
Decision 29 — So and the repeated auxiliary
Read the sentence. One student says, ‘I have submitted the report.’ Another says, ‘So has Mira.’ Decision. This is grammatical. The inverted sequence so has Mira means that Mira has submitted the report too.
Why. Replacing has with does would mismatch the perfect construction and could change the time reading. Transfer test. Make a parallel sentence beginning ‘I can explain the method.’ Which auxiliary would the second speaker repeat?
Decision 30 — Neither and a negative similarity
Read the sentence. A sentence reads, ‘The smaller tank cannot meet the limit, and neither can the older one.’ Decision. No correction is needed. Neither can expresses that the negative property also applies to the second tank.
Why. The inversion after neither is grammatical, and can matches the modal phrase in the first clause. The statement is still a claim that needs measurement. Transfer test. Rewrite with ‘The smaller tank has not passed inspection.’ Which auxiliary fits after neither?
Decision 31 — A negative statement without do-support
Read the sentence. The text says, ‘The sample does not has enough volume.’ Decision. Use ‘The sample does not have enough volume.’
Why. Once does carries present agreement and negation, the lexical verb remains in the base form. It is not has after does. Transfer test. Compare ‘The sample has enough volume’ and its negative. Which verb changes shape?
Decision 32 — A question with lexical have
Read the sentence. A notice asks, ‘Does the tank have a lid?’ Decision. The sentence is grammatical. Here have is a lexical verb meaning ‘possess’; does forms the present question.
Why. Not every appearance of the word have is a perfect auxiliary. Its grammatical role determines how the question is formed. Transfer test. Compare ‘Has the tank been checked?’ There, is has a lexical verb or an auxiliary?
Decision 33 — A misplaced auxiliary in a question
Read the sentence. A report asks, ‘Why the observations were excluded?’ Decision. If it is a direct question, write ‘Why were the observations excluded?’
Why. The past passive auxiliary were precedes the subject in a direct question. With an embedded question, the original order may be appropriate. Transfer test. Now place the clause after ‘We asked why…’ and decide whether the inversion remains.
Decision 34 — A modal perfect
Read the sentence. The sentence reads, ‘The group should have check the readings.’ Decision. Use ‘The group should have checked the readings.’
Why. After a modal followed by perfect have, the lexical verb appears as a past participle. Should have checked describes an action that was advisable but may not have happened. Transfer test. Does this correction prove that the group failed to check? Explain how context and modal meaning affect the inference.
Decision 35 — A conditional auxiliary chain
Read the sentence. A report says, ‘If the team had measured the tank, it would have find the problem.’ Decision. Use ‘It would have found the problem’ in the consequence clause.
Why. The modal perfect construction takes a past participle after have. The hypothetical past condition remains intact; changing it to a present certainty would distort the statement. Transfer test. Compare the assertion ‘The team found the problem’. Why does the conditional sentence not establish that this occurred?
Decision 36 — A final check on rhetorical certainty
Read the sentence. The draft states, ‘The system must have worked because the light was on.’ Decision. The auxiliary structure is grammatical. Do not replace must have worked simply to create a grammatical correction.
Why. The issue, if any, is the strength of the inference from the evidence. This is a reading and reasoning question, not necessarily an auxiliary grammar error. Transfer test. What additional evidence would be needed before a report responsibly claimed that the entire system worked?
A complete passage: ten decisions before the answers
Read this invented notice as one piece of prose before correcting anything. ‘The student committee have chosen a display vessel for the garden. Yesterday, the team did measured the full internal height. The records shows two possible capacities. Does the larger model holds more water at the safe fill line? The staff are check the calculations this morning. One student has been revise the label, and another is preparing the final comparison. The display will can open after the required school review. However, the written proposal did not explains the possible limits. The water have not been approved for drinking. The team is hoping visitors might understands how careful measurements support good decisions.’
Identify ten genuinely grammatical problems. Do not ‘correct’ scientific or administrative claims by guessing new facts. There is one possible disagreement about collective nouns across varieties of English, so use the paragraph’s clearly singular noun phrases or an explicit consistent plural interpretation before assigning a correction. One especially helpful approach is to put every auxiliary and its following lexical verb on a separate line; most of the problems become visible once those pairs are read together.
Model repair of the practice passage
A consistent edited version is: ‘The student committee has chosen a display vessel for the garden. Yesterday, the team did measure the full internal height. The records show two possible capacities. Does the larger model hold more water at the safe fill line? The staff are checking the calculations this morning. One student has been revising the label, and another is preparing the final comparison. The display will be able to open after the required school review. However, the written proposal did not explain the possible limits. The water has not been approved for drinking. The team is hoping visitors might understand how careful measurements support good decisions.’
The grammatical repairs concern has with a singular committee reading, base-form measure after did, plural show, base-form hold after does, the progressive checking, the perfect continuous revising, replacement of the invalid will can stack, base-form explain after did, singular has with water, and base-form understand after might. Notice that some original verb phrases were already correct. Overediting those would waste time and could change the time sequence.
What to do when there are two grammatical alternatives
An editing task is not a free rewriting competition. An original sentence may allow several grammatical phrasings, but the expected repair is the one that addresses the error without unnecessarily changing meaning or the surrounding text. The clause ‘The records show two possible capacities’ has the same subject and purpose as the faulty original. Replacing the whole statement with ‘There are two sizes, but we do not know which is correct’ would introduce a new uncertainty. A fluent sentence that says something different is not a safe answer.
Likewise, the choice between ‘The staff are checking’ and ‘The staff checked’ depends on the time relation. ‘This morning’ alone may fit either when the moment of writing is unknown. The longer passage says the action is ongoing in the present, so the continuous form has a clear purpose. Advanced performance means noticing when a grammatical pattern gives a necessary correction and when it merely offers one of several possible rewrites.
Three patterns worth rehearsing from memory
The first pattern is do/does/did + base form, used for many simple questions and negatives. The second is be + -ing for continuous action or be + past participle for the passive, with additional helpers when the chain is more complex. The third is have + past participle for the perfect, including chains such as has been checked and has been checking. Modals normally take a bare infinitive, although a following perfect or progressive auxiliary may extend the chain.
Do not learn these as isolated decoration. Put a real subject and an actual time relation into each. Write ‘She did not check’, ‘She is checking’, ‘She has checked’ and ‘She should check’ beside one another. Say what each tells the reader, what it leaves unknown and what evidence would distinguish the situations. The meaning check is what turns a memorised grammar table into reliable control.
An independent five-session repair route
In the first session, identify finite auxiliaries in a short passage without editing anything. In the second, practise present and past do-support questions and negatives. In the third, compare is checking, has checked, was checked and has been checked in ordinary contexts. In the fourth, work with modals and short responses, including cases that are already correct. In the fifth, edit an original passage under a modest time limit, then reread every correction for changed meaning.
Keep a small error log: wrong auxiliary agreement, repeated tense after did, inversion in an embedded question, wrong participle after have, or an unnecessary edit of a grammatical clause. If one class of mistakes recurs, practise that distinction with new sentences rather than copying the whole worksheet again. The goal is a stable independent decision, not the number of exercises completed. A learner who can explain why no edit is needed is showing useful restraint.
Continue the English, Mathematics and Science route
For the broader language sequence, use the Secondary English Learning Hub. Return to Volume 0293 when the problem is which pattern follows a lexical verb, and to Volume 0106 when the problem is subject–verb agreement more generally. Volume 0296 shows why careful auxiliary wording also matters when science and mathematics findings are published for others to read.
Use the PSLE Learning Guide when sentence basics are insecure, and Examination Craft when the student knows grammar during revision but loses accuracy under time pressure. A dependable editor sees the shape of the clause, understands the evidence and makes only the correction required. That is a quiet skill. It does not make the sentence grander; it makes it true to what the writer meant.
