How does the hyphen change the meaning in expressions like "high performance" and "high-performance"?

Question

I'm wondering about the distinction between expressions like "high performance" and "high-performance", or "high level" and "high-level" and other similar pairs of words which are sometimes used with a hyphen and sometimes not.

Am I right that without the hyphen, the first word is an adjective and the second a noun, whereas with the hyphen, the pair should be used as an adjective and would need a noun to go with it? Also, am I right that some expressions, such as "high-performance computing" have an established meaning and are usually used with a hyphen?

Examples:

• High-performance is often desired ... (incorrect use)
• High performance is often desired ... (correct use)
• High-performance computing is ... (correct use)
• High performance computing is ... (correct use but not following established norm)

Answer 1

The hyphen is not required in the first pair. As you say, high is simply an adjective and performance is simply a noun which high modifies.

In the second pair, high is again an adjective and performance is a noun functioning as an adjective and together they modify computing. The question to ask is whether the absence of a hyphen between high and performance creates ambiguity. Is it possible that a reader might somehow think that computing is modified independently by both high and performance? Probably not. Nevertheless, as the late R L Trask wrote in ‘The Penguin Guide to Punctuation’:

The hyphen is . . . used in writing compound words which, without the hyphen, would be ambiguous, hard to read or overly long. Here, more than anywhere else in the whole field of punctuation, there is room for individual taste and judgement;

The absence of a hyphen might cause the reader a brief moment’s uncertainty over whether high and computing are to be taken separately or as a whole. If you think that might make the piece ‘hard to read’, then you would be well advised to use the hyphen.

Answer 2

"High performance computing" is potentially ambiguous (both high and performance are acting as adjectives) and might suggest:

• Computing which performs highly
• Computing which calculates performance at heights
• Computing high up (on a shelf or up a mountain) which calculates performance

The hyphen "High-performance computing" avoids the third possibility, as well as signalling that performance is unlikely to be a noun here, and so may help the reader understand what is meant.

Answer 3

I would agree with all that but it's worth remembering that the Oxford University Press style manual says, "If you take hyphens seriously, you will surely go mad".