Something I have noticed whilst proof-reading translations sent by freelance partners over the last months has been the 'grey area' that sometimes crops up surrounding hyphenation in English. Hyphens (not the same as the dash) join two or three words together into a 'compound'. Guidelines on hyphenation can often be found in the dictionary, but not always, and many words lose their hyphens with time. Overuse of hyphens becomes ridiculous, but where they are omitted this can leave meaning ambiguous or may cause your text to strike a native speaker as having "something missing". In this article we will try to provide some rough guidelines for use.

Let us deal firstly with those cases in which rules exist or hyphens are required for reasons of meaning:

1. First and foremost, hyphens should be used as a general rule for compound adjectives to clarify what is being described, e.g. a light blue uniform is not necessarily the same as a light-blue uniform and a slow moving vehicle should probably be written a slow-moving vehicle. Omission in such cases can cause real confusion for the reader.
    
2. Equally important are those hyphens that actually change the meaning of individual words, such as resign / re-sign, recover / re-cover.
    
3. You should also use the hyphen where non-use would render a text ugly or difficult to read, as with double vowels (re-elect).
    
4. Prefixes are always hyphenated before proper names, such as in pro-European.

Another important area of usage of hyphens is that of numbers.

1. Fractions are always hyphenated when attributive, but not when they are used as nouns, e.g. the work is three-quarters finished, but we have seen a rise in production of three quarters.
    
2. One important rule to remember is to hyphenate the numbers between twenty-one and ninety-nine when writing them out in full - a useful tip for filling in cheques in English!
    
3. Compound adjectives containing numbers or formed from numbers also take hyphens: a four-year-old child, a second-class stamp (but not in cases such as two weeks' holiday).

There are also some general rules governing cases in which it is preferred not to use the hyphen:

1. Adverb-adjective modifiers where the adverb ends in -ly do not take a hyphen, as in a highly revered professor (a common pitfall).
    
2. The hyphen is often omitted from frequently used words such as cooperation or skiing.
    
3. The use of hyphens often also depends on grammar. In particular they tend to be omitted where the words in the compound return to their usual grammatical function, for example we have long-term plans, but plans for the long term.

The above provides some general guidelines to using hyphens, although it can in no case claim to be an exhaustive list. The best advice, of course, is always to use a good dictionary (Collins, Oxford, Chambers) together with a solid grammar guide. But you will need your own sense of the English language to determine cases in which you have to use hyphens for the sake of clarity. For example, what would you want your reader to understand by a hard working man?