4.3 Parallel Structure

The Symmetry Requirement

Parallel structure: The student will recognize and correct problems in parallel structure in sentences.

Parallelism is a simple principle with a wide reach: elements that serve the same grammatical function in a sentence must take the same grammatical form. When they do not, the sentence reads as though it lost its footing partway through — and readers feel the stumble even when they cannot name it.

Parallelism in Series

Items joined by and or or must match in form.

✗ The internship involves drafting reports, client interviews, and to attend site inspections.

Three items, three different forms: a gerund phrase, a noun phrase, an infinitive phrase. Repair by choosing one form and holding it:

✓ The internship involves drafting reports, interviewing clients, and attending site inspections. (all gerunds) ✓ The internship involves report drafting, client interviews, and site inspections. (all noun phrases)

Either is correct. Consistency is the requirement, not any particular form.

The Detection Method

The fastest way to test a series is to read each item separately against the stem:

The internship involves... drafting reports. ✓ The internship involves... client interviews. ✓ The internship involves... to attend site inspections. ✗

The third breaks. This works because parallel items must each combine grammatically with the same lead-in.

Parallelism in Clauses

The requirement extends beyond words:

✗ The report concluded that the levee was undersized, that maintenance had lapsed, and inspection records were incomplete.

Two items use that; the third drops it. Either repeat that before all three or use it only before the first:

✓ ...that the levee was undersized, that maintenance had lapsed, and that inspection records were incomplete. ✓ ...that the levee was undersized, maintenance had lapsed, and inspection records were incomplete.

The same all-or-first-only rule governs repeated prepositions and articles:

✗ The grant supported research in Ohio, Michigan, and in Indiana. ✓ ...in Ohio, Michigan, and Indiana. — or — ...in Ohio, in Michigan, and in Indiana.

Correlative Conjunctions

Correlatives come in fixed pairs, and the structures following each half must match exactly:

✗ The grant not only funded the survey but also the equipment.

After not only comes a verb phrase (funded the survey); after but also comes a noun phrase (the equipment). Mismatch. Two repairs:

✓ The grant funded not only the survey but also the equipment. (noun ↔ noun) ✓ The grant not only funded the survey but also purchased the equipment. (verb ↔ verb)

The first repair is the more elegant move and the one students overlook: rather than expanding the second half, shift the correlative rightward so the shared verb sits before it.

Also note the fixed pairings. Neither pairs with nor, never with or; not only pairs with but also, not with and also.

Parallelism in Comparisons

Comparisons must set logically equivalent things side by side. This overlaps with logical comparison in the usage category, and it appears on the test in both guises.

✗ The turbine's output exceeded the older model.

This compares an output to a model — a quantity to a machine. Repair:

✓ The turbine's output exceeded that of the older model. ✓ The turbine's output exceeded the older model's.

The repair devices are worth memorizing: that of (singular), those of (plural), or a possessive.

✗ Unlike most community colleges, the district's enrollment grew during the recession.

This compares colleges to an enrollment figure. Repair: Unlike most community colleges, the district enrolled more students during the recession.

Comparison signals that should trigger a parallelism check: than, as, like, unlike, similar to, compared with, in contrast to.

Parallelism With And Joining Verbs

A compound predicate requires matching verb forms in tense and voice:

✗ The committee reviewed the proposal and is recommending approval.

Past tense joined to present progressive. Unless the passage genuinely marks a time shift, make them agree:

✓ The committee reviewed the proposal and recommended approval.

✗ The samples were collected in June and the lab analyzed them in July.

Passive joined to active. Consistent voice reads better:

✓ The samples were collected in June and analyzed in July.

Why Parallelism Carries Weight

Parallelism is one of the few conventions errors that damages meaning as well as form. A faulty comparison can state something false — the turbine's output exceeded the older model literally claims a number is larger than a machine. A broken series can obscure which items belong together. That is why parallelism items appear across both the Sentence Structure category and, as logical comparison, the Conventions of Usage category.

A practical scanning habit: whenever you see and, or, a correlative pair, or a comparison word, stop and check that the elements on each side match in form.