Preserve grammatical form across a list
Parallel structure connects comparable ideas using corresponding grammatical forms. A list of actions can use infinitive phrases, gerund phrases or another consistent pattern. The aim is not to force every sentence into one template, but to keep the coordinated elements in the relationship the sentence establishes. Meaning and form must agree. Worked example:“The group plans to sort folders, to index photographs, and to store receipts.” The three actions share the to-plus-verb form. Replacing the last item with storage of receipts changes that form. In a different sentence beginning“The work includes sorting, indexing, and storing,” gerunds would be appropriate. Thus a form that is correct somewhere can be a poor fit in the sentence being tested. Find the words coordinated by and or or, and compare those units rather than nearby nouns. Read the sentence once for meaning and once for pattern. In the diagnostic, the first two actions establish the pattern clearly; you need not revise their subjects or invent punctuation. Explain what grammatical type each distractor supplies and why it does not fit this particular series. This distinguishes a rule-based answer from a vague judgment that one choice merely sounds better.
Choose the completion that makes all three listed actions parallel: “The volunteers agreed to label packets, to weigh samples, and _____.”
- The three actions share the infinitive pattern: to label, to weigh, to record. The grammatical relationship, rather than the subject matter, determines the matching completion.
Compare the other answer choices
This finite verb does not match the preceding “to label” and “to weigh” phrases.
This noun phrase names a record rather than supplying a third parallel action.
This gerund phrase changes form after two infinitive phrases.
Try it, then explain it.
Complete a short set without looking at the example. After each answer, explain which evidence or rule supports your decision and why the alternatives do not fit.
Sources & authorship
Original Slope explanations and examples. References support the concepts; they are not the source of copied questions. Independent educator review is pending.
Mills/LibreTexts—Parallelism