Three general principles are laid down by Mr. F. Horace Teall which will be found useful, though they must be supplemented in practice by more specific rules which will be given later. They are as follows:
I All words should be separate when used in regular grammatical relations and construction unless they are jointly applied in some arbitrary way.
An iron fence means a fence made of iron. The meaning and construction are normal and the words are not compounded.
An iron-saw means a saw for cutting iron. The meaning is not the same as iron saw which would mean a saw made of iron. The hyphenated compound indicates the special meaning of the words used in this combination.
Ironwood is a specific name applied to a certain kind of very hard wood. Hence, it becomes a single word compounded but without a hyphen. Either of the other forms would be ambiguous or impossible in meaning.
II Abnormal associations of words generally indicate unification in sense and hence compounding in form.
A sleeping man is a phrase in which the words are associated normally. The man sleeps.
A sleeping-car is a phrase in which the words are associated abnormally. The car does not sleep. It is a specially constructed car in which the passengers may sleep comfortably.
A king fisher might be a very skilful fisherman. A kingfisher is a kind of bird. Here again we have an abnormal association of words and as the compound word is the name of a specific sort of bird there is no hyphen. A king-fisher, if it meant anything, would probably mean one who fished for kings, as a pearl-diver is one who dives for pearls.
III Conversely, no expression in the language should ever be changed from two or more words into one (either hyphenated or solid) without change of sense.