§ 1.The modal wordsexpress the attitude of the speaker to the reality, possibility or probability, of the action he speaks about.
§ 2. According to their meaning modal words fall under the following main groups:
(1) words expressing certainty(certainly, surely, assuredly, of course, no doubt, apparently, undoubtedly, etc.);
(2) words expressing supposition(perhaps, maybe, possibly, probably, etc.);
(3) words showing whether the speaker considers the action he speaks about desirable or undesirable(happily — unhappily; luckily — unluckily; fortunately — unfortunately).
§ 3. In the sentence modal words are used as parentheses.1Sometimes they are used as sentence-words.2
1 See Chapter XV, The Simple Sentence.
2 Modal words used as sentence-words are similar to the words yes and no expressing affirmation and negation, which are also sentence-words.
Certainly you’ll admit we could finish all this in a month. (Wilson)
“Will you allow me to detain you one moment,” said he. “Certainly,”replied
the unwelcome visitor. (Dickens)
§ 4. Most modal words have developed from adverbs, so very often there exists a formal identity between modal words and adverbs. For instance such modal words as certainly, surely, happily are homonymous with the adverbs certainly, surely, happily.
Such modal words as possibly, probably, indeed, also derived from adverbs, have no corresponding homonymous adverbs because the latter ceased to be used in Modern English.
Though formally identical with adverbs, modal words differ from them in meaning and syntactical function.
If he were not married as happilyas he was, might notsomething come of it?
(Dreiser) (ADVERB)
...she hauled me to the washstand, inflicted a merciless, but happilybrief
scrub on my face and hands with soap water, and a coarse towel... (Ch.
Bronte) (MODAL WORD)
Lamlein rose. “We have fulfilled our obligations,” he said pompously, and yet
not quite certainly.(Heym) (ADVERB)
Soames smiled. Certainly, uncle Jolyon had a way with him. (Galsworthy)
(MODAL WORD)
Slowly, surely, with the secret inner process that works the destruction of an
old tree, the poison of the wounds to his happiness, his will, his pride, had
corroded the comely edifice of his philosophy. (Galsworthy) (ADVERB)
Over the ridge she would find him. Surelyshe would find him over the ridge.