Expressions like a shárp edgéd instrument, meaning an instrument that is sharp and has edges, as opposed to a shárp-edged instrument, meaning an instrument with sharp edges, further exemplify this difference.
Subject to four small classes of exceptions, it may be laid down, that, in the English language, there is no composition unless there is either a change of form or a change of accent.
The reader is now informed, that unless, in what has gone before, he has taken an exception to either a statement or an inference, he has either seen beyond what has been already laid down by the author, or else has read him with insufficient attention. This may be shown by drawing a distinction between a compound form and a compound idea.
In the words a red house, each word preserves its natural and original meaning, and the statement is that a house is red. By a parity of reasoning a mad house should mean a house that is mad; and, provided that each word retain its natural meaning and its natural accent, such is the fact. Let a house mean, as it often does, a family. Then the phrase, a mad house, means that the house, or family, is mad, just as a red house means that the house is red. Such, however, is not the current meaning of the word. Every one knows that a mad house means a house for mad men; in which case it is treated as a compound word, and has a marked accent on the first syllable, just as Límehouse has. Now, compared with the word red house, meaning a house of a red colour, and compared with the words mad house, meaning a deranged family, the word mádhouse, in its common sense, expresses a compound idea; as opposed to two ideas, or a double idea. The word beef steak is evidently a compound idea; but, as there is no disparity of accent, it is not a compound word. Its sense is compound; its form is not compound, but double. This indicates the objection anticipated, which is this: viz., that a definition, which would exclude such a word as beef steak from the list of compounds, is, for that very reason, exceptionable. I answer to this, that the term in question is a compound idea, and not a compound form; in other words, that it is a compound in logic, but not a compound in etymology.
Now etymology, taking cognisance of forms only, has nothing to do with ideas, except so far as they influence forms.
Such is the commentary upon the words, "treating the combination as a single term;" in other words, such the difference between a compound word and two words. The rule, being repeated, stands (subject to the four classes of exceptions) thus: There is no true composition without either a change of form or a change of accent. As I wish to be clear upon this point, I shall illustrate the statement by its application.
The word trée-rose is often pronounced trée róse; that is, with the accent at par. It is compound in the one case; it is two words in the other.
The words mountain ash and mountain height are generally (perhaps always) pronounced with an equal accent on the syllables mount- and ash, mount- and height, respectively. In this case the word mountain must be dealt with as an adjective, and the words considered as two. The word moúntain wave is often pronounced with a visible diminution of accent on the last syllable. In this case there is a disparity of accent, and the word is compound.
[§ 417]. The following quotation indicates a further cause of perplexity in determining between compound words and two words:—
1.