OBS. 6.—­Beside the instances already mentioned, of words used both adjectively and adverbially, our dictionaries exhibit many primitive terms which are to be referred to the one class or the other, according to their construction; as, soon, late, high, low, quick, slack, hard, soft, wide, close, clear, thick, full, scant, long, short, clean, near, scarce, sure, fast; to which may as well be added, slow, loud, and deep; all susceptible of the regular form of comparison, and all regularly convertible into adverbs in ly; though soonly and longly are now obsolete, and fastly, which means firmly, is seldom used.  In short, it is, probably, from an idea, that no adverbs are to be compared by er and est unless the same words may also be used adjectively, that we do not thus compare lately, highly, quickly, loudly, &c., after the example of Milton.  But, however custom may sanction the adverbial construction of the foregoing simple terms, the distinctive form of the adverb is in general to be preferred, especially in prose.  For example:  “The more it was complained of, the louder it was praised.”—­Daniel Webster, in Congress, 1837.  If it would seem quaint to say, “The loudlier it was praised,” it would perhaps be better to say, “The more loudly it was praised;” for our critics have not acknowledged loud or louder to be an adverb.  Nor have slow and deep been so called.  Dr. Johnson cites the following line to illustrate the latter as an adjective: 

   “Drink hellebore, my boy! drink deep, and scour thy brain.  DRYDEN.”
        —­Joh.  Dict., w.  Deep.

    “Drink hellebore, my boy! drink deep, and purge thy brain.”
        —­Dryd.  IV.  Sat. of Persius.

OBS. 7.—­In some instances, even in prose, it makes little or no difference to the sense, whether we use adjectives referring to the nouns, or adverbs of like import, having reference to the verbs:  as, “The whole conception is conveyed clear and strong to the mind.”—­Blair’s Rhet., p, 138.  Here clear and strong are adjectives, referring to conception; but we might as well say, “The whole conception is conveyed clearly and strongly to the mind.”  “Against a power that exists independent of their own choice.”—­Webster’s Essays, p. 46.  Here we might as well say, “exists independently;” for the independence of the power, in whichever way it is expressed, is nothing but the manner of its existence.  “This work goeth fast on and prospereth.”—­Ezra.  “Skill comes so slow, and life so fast doth fly.”—­Davies.  Dr. Johnson here takes fast and slow to be adjectives, but he might as well have called them adverbs, so far as their meaning or construction is concerned.  For what here qualifies the things spoken of, is nothing but the manner of their motion; and this might as well be expressed by the words, rapidly, slowly, swiftly.  Yet it ought to be observed, that this does not prove the equivalent words to be adverbs, and not adjectives.  Our philologists have often been led into errors by the argument of equivalence.