Clear Technical Writing
Special Topics

Compound Adjectives

This lesson is about words we pile up in front of a noun and then worry about whether we should use a hyphen.

Every time we use a compound adjective we are doing three things to Sentence E so that we might have Sentence S:

E. They own equipment that uses a high level of technology.

S. They own high-tech equipment.

Here is what we are doing:

1. We condense an Explicit description into a Succinct description.

2. We promote the Succinct description to sit in front of the noun.

3. We mark the Succinct description to show the reader that it expresses a single thought.

The most authoritative source on this topic is the Gregg Reference Manual, and it begins its exhaustive treatment of compound adjectives with this:

No aspect of style causes greater difficulty than compound adjectives.

Whenever you have strong doubts about hyphenating a compound adjective, remember that Sentence E is always available as a backup.

Let's concentrate on special cases.

Words that end in ly

She is a highly valued employee. He is a friendly-sounding salesperson.

highly valued = adverb + participle

friendly-sounding = adjective + participle

There are few adjectives that end in ly. So most of the time when you assemble a compound adjective starting with an ly word, it is an adverb. We do not use a hyphen in this case. Here is why:

highly .. employee (does not make sense)

friendly .. salesperson (does make sense)

When you are not sure about a compound adjective that starts with an ly word, place your finger over the next word in the compound and see if the remaining words make sense.

Compounds well established

When a compound adjective is a well-known phrase, it does not use a hyphen.

I used my word processing program to write my branch office report about my inspection of the nuclear power plant.

When you are confident most readers understand the concept or recognize the organization, it's safe to omit the hyphen. More examples:

life insurance policy

public relations director

accounts receivable invoice

Exception: When a noun-noun combination uses two words of similar concept and rank, we do use a hyphen.

input-output device

cost-benefit analysis

space-time continuum

Quantity, Percent, Money

Compound adjectives formed from a number and a noun use hyphens, even if they are long.

In 16 minutes, we filled the 50-gallon tank using a 12-liter-per-hour flow rate.

Because of that 25-cent coupon, we suffered a $75-a-week deficit.

With a thousand 40-foot containers, we had a 25-thousand-ton shipment.

The most significant exceptions have to do with percent and money.

We had a 10 percent increase in sales.

That resulted in a $2 million profit.

We probably have accountants to blame (or thank) for these exceptions.

Edit your writing by spotting hyphen problems.

We worked with clearly-defined requirements to design our mass-production facility. We got a 5 year loan from the commercial bank, which charges 4-percent interest.
  

Lesson: Compound Adjectives
Module: Special Topics
Course: Clear Technical Writing