Parallel Constructions

The following sentence elements indicate parallel constructions:

(1) Coordinate conjunctions (and, but, or, for, nor, yet). A shift in verb tense, voice, or mood, after a coordinating conjunction, violates parallelism and may create difficulties in understanding.

Incorrect
Limestones in massive beds and thin layers of sandstones.

Correct
Limestones in massive beds and sandstones in thin beds.

(2) Correlative conjunctions (both…and, either…or, if…than, neither…nor, not only…but also). If a verb follows one, a verb should follow the other; if a prepositional phrase follows one, a prepositional phrase should follow the other. Repair of faulty parallelism may require only transposition or addition of a word or two.

Incorrect
This nation not only has achieved great things in science but also in the arts.

Correct
This nation has achieved great things not only in science but also in the arts.

(3) And which, and who, and that, but which, but who, and but that need preceding which, who, or that.

Incorrect
This basin, the largest and which contains the principal oil field, is in the western part of the country.

Correct
This basin, which is the largest and which contains the principal oil field, is in the western part of the country.

(4) Items in a list, table, or series should be in the parallel format.

Incorrect
(a) Laboratory equipment should be assembled; (b) then arrange samples in proper sequence; (c) tests are run; (d) we recommend that results then be recorded.

Correct
(a) Assemble laboratory equipment, (b) arrange samples in proper sequence; (c) run tests, (d) record results.

(5) Expressions of comparison and contrast.

Incorrect
The instruments on Skylab were more complex than the ERTS payload.

Correct
The instruments on Skylab were more complex than those on ERTS.