s. 416. The difference between a compound word and two words is greatest where the first is an adjective. This we see in comparing such terms as the following: _bl['a]ck b['i]rd_, meaning a _bird that is black_, with _bl['a]ckbird_=the Latin _merula_; or _bl['u]e b['e]ll_, meaning a _bell that is blue_, with _bl['u]ebell_, the flower. {359} Expressions like _a sh['a]rp edg['e]d instrument_, meaning _an instrument that is sharp and has edges_, as opposed to a _sh['a]rp-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 _L['i]mehouse_ 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 _m['a]dhouse_, 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. {360} Now etymology, taking cognisance of forms only, has nothing to do with ideas, except so far as they influence forms.