I have not time to go into a thoro investigation of the mistakes into which grammarians have fallen in their attempts to explain this “part of speech.”  Mr. Murray says they “seem originally to have been contrived to express compendiously in one word, what must otherwise have required two or more; as, “he acted wisely.”  They could have been “contrived” for no such purpose, for we have already seen that they are made up of various words combined together, which are used to express relation, to define or describe other things.  Take the very example Mr. M. has given. Wisely is made up of two words; wise and like.  “He acted wisely,” wise-like.  What did he act? Wisely, we are taught, expresses the “manner or quality” of the verb act.  But act, in this case, is a neuter or intransitive verb, and wisely expresses the manner of action where there is none!  But he must have acted something which was wise like something else.  What did he act?  If he produced no actions, how can it be known that he acted wisely or unwisely? Action or acts is the direct object of to act.  Hence the sentence fully stated would stand thus:  “He acted acts or actions like wise actions or acts.”  But stated at length, it appears aukward and clumsy, like old fashioned vehicles.  We have modified, improved, cut down, and made eliptical, all of our expressions, as we have previously observed, to suit the fashions and customs of the age in which we live; the same as tailors cut our garments to correspond with the latest fashions.

“The bird sings sweetly.”  The bird sings songs, notes, or tunes, like sweet notes, tunes, or songs.  The comparison here made, is not in reference to the agent or action, but the object of the action; and this explains the whole theory of those adverbs, which are said to “qualify manner” of action.  We have already seen that no action, as such, can exist, or be conceived to exist, separate(-ed) from the thing or agent which acts; and such action can only be determined by the changed or altered condition of something which is the object of such action.  How then, can any word, in truth, or in thought, be known to qualify the action, as distinct from the object or agent?  And if it does not in fact, how can we explain words to children, or to our own minds, so as to understand what is not true?

Hence all words of this character are adjectives, describing one thing by its relation or likeness to another, and as such, admit of comparison; as, a likely man, a very likely man, a likelier, and the likeliest man.  “He is the most likely pedlar I ever knew.”  “He is more liable to be deceived.”  “A lively little fellow.”  “He