Clients sometimes ask why I’ve hyphenated a compound adjective (‘high-performance computing’, ‘value-added tax’, ‘industry-leading SLAs’, etc). While I could no doubt haul out the Economist style guide or the Chicago Manual of Style or some other ‘authority’ on the matter, I don’t think that’s really answering the question.
It’s not about ‘rules’
Here at HN, we’re not really interested in whether something is a ‘rule’ so much as whether it helps readers follow what we’re trying to say. We’re keenly aware that because language is always evolving, today’s ‘rule’ is likely to be no more than a preference tomorrow and an outdated way of doing things by next week. If clarity of meaning is best achieved by adhering to a ‘rule’ of grammar, then we’ll be passionate about that point; not because it’s a ‘rule’ or the ‘right’ way to do it, but because adherence to common practice aids clear communication.
So, when it comes to explaining why I’ve hyphenated a compound adjective, I might cite common guidance across style guides as good evidence for a practice so common that to go against it would be needlessly confusing. But it’s not as if I’ve memorised a bunch of style-guide rules for hyphenation. When I hyphenate, I’m applying an underlying principle about communicating clearly, which is simply this.
It’s about helping the reader to follow what we’re saying
If there’s any chance of the reader stumbling over a sentence containing a compound adjective, even for a fraction of a second, then I’ll hyphenate it. The hyphen simply ‘chunks’ words to help the meaning come through clearly.
Imagine reading a sentence that starts: ‘We give you high performance.’
It’s a perfectly normal, good sentence where the object of the sentence is a standard construction of [adjective noun]. As you read it, you take in the thought (we give you high performance) and, because it’s a well-formed, perfectly complete sentence fragment, you might well expect it to be followed by a full stop, or a conjunction (and, because, if, etc), or maybe a comma if ‘performance’ is the first in a list of nouns modified by ‘high’ (eg, ‘we give you high performance, availability and resilience’).
But what if that’s not what you get? What if, without any comma, you get another noun: ‘connection’.
It’s not usual for the direct object of a sentence to be constructed as [adjective noun noun]. So you might stumble a little, just for a second. Maybe you think: ‘is there an ‘and’ missing ie it should be ‘we give you high performance and connection’?
The problem is that there’s nothing to signify in advance – until you’ve already read the extra noun and stumbled over it – that, in this case, the two words ‘high’ and ‘performance’ are not an adjective modifying a noun, but a compound adjective modifying the noun ‘connection’. Hyphenating this kind of compound adjective simply avoids any chance of that stumble; thus: ‘We give you high-performance connection’ (ie, a connection with high performance).
Erring on the side of caution
Wherever I use a hyphen, it’s usually to help readers in a similar way by chunking words that otherwise might be stumbled over. Even if we (or our clients) don’t stumble over them, if there’s a chance that someone completely fresh to it might, I’d tend to err on the side of caution and include the hyphen. If there’s no chance of ambiguity or uncertainty, I leave it out.