Hyphen ( - )

The hyphen is a joining signal, in contrast to an em dash, which is a separator (see section 5 for discussion of dashes). Its main use is to link two or more words together to form a compound adjective (or compound modifier) to describe (qualify or modify) another word:

As is discussed in section 4.5, if you intend each of several adjectives in a sequence separately to modify a noun, you need no hyphens. Simply help your reader by separating the adjectives with commas:

But if you intend two or more words to form a compound to modify a noun, use one or more hyphens to signal the compound:

However, if you frequently link two or three words with hyphens to form pre-modifying units, as in the last two examples, it is probable that you will create an uncomfortable, ‘lumpy’ text. Preferably, reconstruct your statement:

There is a conventional departure from this rule: you do not need to put commas after number adjectives and colour adjectives when you use them in combination with other modifiers, provided that there is no possibility of the number adjective or colour adjective being misinterpreted as part of a compound:

But when the number or colour is intended as part of a compound, a hyphen is vital:

There is often an interesting difference of meaning intended in three-word groups that consist of two adjectives in front of a noun. Most frequently, the two adjectives modify the noun individually, and (as described in section 4.5) it is helpful to signal that fact by separating the adjectives with commas:

Occasionally, however, the first word modifies the idea expressed by the second and third together:

Here, the intended meaning is ‘the primary controller that has failed’, not ‘the failed primary-controller’. Conventionally, when two adjectives appear before a noun in this way, and the first modifies the idea expressed by the second modifier and the noun combined, no hyphen or comma is used:

Use ‘suspended’ hyphens to create compounds in which two or more adjectives or numbers are attached to one other word:

But do not write:

write:

However, interpretation of structures using suspended hyphens may be difficult for some readers working in English as their second or third language, and it is wise to re-word your thoughts if you can do so comfortably:

A word of warning: remember to supply a hyphen when you want to create a compound consisting of a noun plus an -ing word-form. As our eyes and minds arrive at the sequence of words ‘men behaving badly’, our expectations about normal word-sequences in English lead us to interpret men as the subject of the group, behaving as the verb telling us what they are doing, and badly as an adverb telling us about the way they are behaving. Similarly, when we arrive at ‘librarians seeking information’, normal expectations lead us to interpret librarians as the subject of the group, seeking as the verb, and information as the object they are seeking. Because of normal expectations, the following hyphen-less sequences create images in our minds that disturb, albeit only momentarily, readers’ concentration on the discourse of the text.