Parallel Structure: Writing Balanced Sentences in OET Letters

Parallel structure in OET writing is one of those errors that doesn’t look like a grammar mistake at all — every word is spelled correctly, every verb is conjugated, and the sentence still reads as slightly off. That’s because the problem isn’t inside any single word; it’s in the mismatch between items that are supposed to match. A symptom list, a set of discharge instructions, or a comparison between two treatments all rely on parallel structure to hold together, and clinical letters are dense with exactly this kind of listing. Get it wrong three or four times in one letter and the Language criterion notices a pattern, not a slip.

Watch the full breakdown: Grammar Quick Fix #3 works through parallel structure using symptom lists and discharge instructions from real OET writing tasks.

Why does parallel structure break down so often in OET letters?

OET writing tasks are built around lists by nature. Case notes hand you a cluster of symptoms, a sequence of investigations, a run of medications, or a set of instructions for the receiving clinician or the patient — and the natural way to report any of that in a letter is as a list joined by commas and a final “and.” The letter genre almost forces you into parallel constructions dozens of times per script.

The trouble is that candidates draft under time pressure, and a list is exactly where drafting speed causes trouble: you write the first item as a noun, the second item as a noun, and by the third item your attention has moved ahead to the next sentence, so you write what you’re actually thinking — a full clause — instead of continuing the noun pattern. “She presented with fever, cough, and was short of breath” is the textbook version of this: two nouns, then a full verb phrase where a third noun was expected. Nothing about it looks obviously wrong on a first read because each piece, in isolation, is grammatically fine. It’s only wrong in relation to the other items around it.

What exactly counts as “parallel” in a sentence?

Parallel structure requires that every item filling the same grammatical slot in a sentence takes the same form. That form can be almost anything — a noun, a gerund (-ing form), a bare infinitive, a past participle, a prepositional phrase — as long as it’s consistent across the whole list or pair.

Noun lists:

• Not parallel: The patient complained of headache, nausea, and feeling dizzy.
• Parallel: The patient complained of headache, nausea, and dizziness.

Gerund lists (common when listing ongoing management actions):

• Not parallel: Management includes monitoring blood glucose, adjusting insulin doses, and to review her diet.
• Parallel: Management includes monitoring blood glucose, adjusting insulin doses, and reviewing her diet.

Infinitive lists (common in instructions and recommendations):

• Not parallel: She was advised to rest, increasing her fluid intake, and monitor her temperature.
• Parallel: She was advised to rest, increase her fluid intake, and monitor her temperature.

Notice that once “to” introduces the first verb in an infinitive list, the items that follow only need the bare verb — “to rest, increase, and monitor” — not “to rest, to increase, and to monitor” repeated each time, though repeating “to” throughout is also acceptable as long as it’s consistent. What breaks the parallel is switching form partway through, not the choice of form itself.

How does this show up in symptom and history lists specifically?

Symptom lists are the single most common place parallel structure fails in OET letters, because case notes themselves are often written in fragments and abbreviations that don’t map cleanly onto full sentences. A candidate converting “SOB, chest pain, sweating ++” into prose has to decide on a consistent grammatical form for all three, and it’s easy to let one item slip into a different shape:

That last example is worth a closer look, because the fix isn’t always to lengthen the odd item out — sometimes it’s to find a single adjective that matches the others instead of expanding the whole list into clauses. “Pyrexial” matches “pale” and “tachycardic” as a one-word adjective; rewriting the first two items into verb phrases to match “had a low-grade fever” would also technically fix the parallelism, but it produces a clunkier sentence. When you spot a mismatch, check both directions before deciding which item is the odd one out.

How does this show up in discharge and management instructions?

Instruction lists in discharge letters and referral letters carry the same risk, and here the stakes are slightly different: a reader working through a numbered or comma-separated list of instructions relies on consistent grammar to parse the list quickly. A mismatched item forces a re-read.

• Not parallel: The patient should continue her current medication, attend physiotherapy twice weekly, and it is recommended that she avoid heavy lifting.
• Parallel: The patient should continue her current medication, attend physiotherapy twice weekly, and avoid heavy lifting.

The unparallel version buries the third instruction inside a passive “it is recommended that” clause that doesn’t match the first two, which are direct verb phrases following “should.” Stripping it back to a bare verb — “avoid heavy lifting” — restores the pattern and, as a side effect, shortens the sentence, which also helps under the Conciseness dimension of Language.

What about “not only… but also” and other correlative pairs?

Correlative conjunctions — “not only… but also,” “either… or,” “neither… nor,” “both… and” — require the same grammatical form on both sides of the pair, and OET letters use them more than candidates realise, especially when summarising a patient’s combined presentation or a combined treatment plan.

• Not parallel: She has not only lost weight but also her appetite has decreased.
• Parallel: She has not only lost weight but also lost her appetite.
• Or, restructured: She has experienced not only weight loss but also decreased appetite.

The test is the same as for any list: read each half of the pair as if it directly completed the stem before the conjunction, and check that both halves take the same grammatical shape.

A quick self-check before you submit

Go through your draft and mark every list of three or more items joined by commas, every pair joined by “and,” “or,” or “but,” and every correlative construction. For each one, isolate the sentence stem and read each item onto it individually. If every version sounds complete and grammatically identical in form, the list is parallel. If one item breaks the pattern — switches from noun to verb, from active to passive, from a phrase to a full clause — rewrite that one item to match the others, not the other way around, unless the odd item is actually the more natural core of the list.

This check pairs well with a broader cohesion pass — our connectors and cohesion in OET writing guide covers how linking words hold sentences together beyond the list level, and the 8 grammar errors that cost Language marks places parallel structure alongside the other patterns examiners flag most consistently. The Language criterion breakdown explains how grammatical range and control are weighted at each band, which is exactly where a mismatched list does its damage.

Why this is worth fixing as a habit, not a one-off edit

Parallel structure errors rarely appear once in a letter. Because case notes hand you list after list — symptoms, then investigations, then medications, then instructions — a candidate who doesn’t have the check automated will repeat the same kind of slip four or five times across one script, and examiners read for exactly this kind of repeated pattern rather than treating each instance as an isolated mistake. A letter with five lists, three of them broken in the same way, reads as a genuine control gap under Language even if every individual sentence is otherwise fluent. Our OET writing correction service checks structural consistency like this across a full letter alongside the other five criteria, so a pattern like unmatched lists gets flagged and corrected before it costs a band.