Keeping it straight: Parallel structureOctober 31, 2011
Each week or so, I try to email my team of authors a writing tip that focuses on typical errors I find in some of their writing. Last week’s tip was on parallel structure. I’ve reproduced it here after removing any identifying information. The examples are from the oil and gas industry, but the same writing principles apply no matter what industry you’re working in.
To understand parallel structure, I’ll show you some examples that aren’t parallel, then describe how to fix them.
Let me give you an example of non parallel structure that I saw recently:
The […] Plant is designed to remove CO2 from the feed gas, compressed and then injected 2.5 km underground into the […] Formation.
The bits that make this sentence sounds awkward are the bits that’s aren’t ‘parallel’; i.e. ‘remove’, ‘compressed’, ‘injected’. These verbs are all over the place – ‘to remove’ is in the future tense (something will happen), whereas ‘compressed’ and ‘injected’ are in the past tense (something has happened); present tense (happening now) would be words like ‘compresses’ or ‘compressing’.
To make this sentence ‘parallel’, I pick one verb tense and stick to it for all verbs in that sentence. So, this sentence could be rewritten in two different ways, depending on the context of the sentences around it:
- Future tense: ‘The […] Plant is designed to remove CO2 from the feed gas, compress it, and then inject it into the […] Formation, 2.5 km underground.’
- Present tense: ‘The […] Plant removes CO2 from the feed gas, compresses it, and then injects it into the […] Formation, 2.5 km underground.’
Here’s another example:
Examples of prevention measures include leak minimisation, minimisation of hazardous inventory, optimising layout design and reducing manning levels.
And here it is reworded so that the verb tenses are parallel:
Examples of prevention measures include minimising leaks, minimising hazardous inventory, optimising layout design, and reducing manning levels.
Another parallel alternative could have been:
Examples of prevention measures include leak minimisation, hazardous inventory minimisation, layout design optimisation, and manning levels reduction.
However, I found that alternative to be very clunky, so I went with the ‘-ing’ verbs instead.
And here’s a final example:
The purposes of the […] Facilities are to:
- receive the raw feed…
- slug storage capacity…
- reduce the gas pressure…
- liquid pressure reduction
- dedicated hydrocarbon/MEG aqueous phase separation
- produce a stabilised condensate stream…
- temporary storage for liquids…
You can often figure out where the structure isn’t parallel by splitting a list of items into bullet points, then looking at the first word or two of each point. Here’s that example above made parallel (strikethroughs = unnecessary words; italics = words I added to make the structure parallel; I removed other words that weren’t necessary for this tip):
purposes of the[…] Facilities are to:
- receive the raw feed ….
- provide slug storage capacity …
- reduce the gas pressure …
- reduce the liquid pressure
- provide dedicated facilities for hydrocarbon/MEG aqueous phase separation
- produce a stabilised condensate stream …
- provide temporary storage for liquids ….
Notice how all the bullet points are now parallel — each starts with a verb (receive, provide, reduce, produce), and each verb is the same tense. And each bullet point could now stand alone with the introductory sentence fragment to make a complete sentence (e.g. The […] Facilities provide slug storage capacity… is a sentence, whereas The […] Facilities slug storage capacity… isn’t).
Parallel structure makes your writing easier to read and understand because your reader doesn’t have to stop and try to figure out what you are trying to say.
See also these blog posts of mine: