(1) Declarative
(2) Interrogative
(3) Imperative
Sentences belonging to the several types differ from each other in some grammatical points, too. Thus, interrogative sentences are characterized by a special word order. In interrogative sentences very few modal words are used, as the meanings of some modal words are incompatible with the meaning of an interrogative sentence. It is clear that modal words expressing full certainty, such as certainly, surely, naturally, etc., cannot appear in a sentence expressing a question. On the other hand, the modal word indeed, with its peculiar shades of meaning, is quite possible in interrogative sentences, for instance, Isn't so indeed? (SHAKESPEARE)
There are also sentences which might be termed semi-interrogative. The third sentence in the following passage belongs to this type:
«Well, I daresay that's more revealing about poor George than you. At any rate, he seems to have survived it». «Oh, you’ve seen him»? She did not particularly mark her question for an answer, but it was, after all, the pivot-point, and Bone found himself replying – that indeed he had. (BUECHNER) The sentence Oh, you’ve seen him? is half-way between the affirmative declarative sentence, You have seen him, and the interrogative sentence, Have you seen him? Let us proceed to find out the precise characteristics of the sentence in the text as against the two sentences just given for the sake of comparison. From the syntactical viewpoint, the sentence is declarative, as the mutual position of subject and predicate is, you have seen, not have you seen, which would be the interrogative order. In what way or ways does it, then, differ from a usual declarative sentence? That is where the question of the intonation comes in. Whether the question mark at the end of the sentence does or does not mean that the intonation is not that typical of a declarative sentence, is hard to tell, though it would rather seem that it does. To be certain about this a phonetic experiment should be undertaken, but in this particular case the author gives a context which itself goes some way toward settling the question. The author's words, She did not particularly mark tier question for an answer, seem to refer to the intonation with which it was pronounced: the intonation must not have been clearly interrogative, that is not clearly rising, though it must have differed from the regular falling intonation to some extent: if it had not been at all different, the sentence could not have been termed a «question», and the author does call it a question. Reacting to this semi-interrogative intonation, Bone (the man to whom the question was addressed) answered in the affirmative. It seems the best way, on the whole, to term such sentences semi-interrogative. Their purpose of course is to utter a somewhat hesitating statement and to expect the other person to confirm it.
Imperative sentences also show marked peculiarities in the use of modal words. It is quite evident, for example, that modal words expressing possibility, such as perhaps, maybe, possibly, are incompatible with the notion of order or request. Indeed, modal words are hardly used at all in imperative sentences.
The notion of exclamatory sentences and their relation to the three established types of declarative, interrogative, and imperative sentences presents some difficulty. It would seem that the best way to deal with it is this. On the one hand, every sentence, whether narrative, interrogative, or imperative, may be exclamatory at the same time, that is, it may convey the speaker's feelings and be characterized by emphatic intonation and by an exclamation mark in writing. This may be seen in the following examples: But he can't do anything to you! (R. WEST) What can he possibly do to you! (Idem) Scarlett, spare me! (M. MITCHELL)
On the other hand, a sentence may be purely exclamatory, that is, it may not belong to any of the three types classed above. This would be the case in the following examples: «Well, fiddle-dee-dee!» said Scarlett. (M. MITCHELL) Oh, for God's sake, Henry! (Idem)
However, it would perhaps be better to use different terms for sentences which are purely exclamatory, and thus constitute a special type, and those which add an emotional element to their basic quality, which is either declarative, or interrogative, or imperative. If this view is endorsed, we should have our classification of sentences according to type of communication thus modified:
(1) Declarative (including emotional ones)
(2) Interrogative (including emotional ones)
(3) Imperative (including emotional ones)
(4) Exclamatory
This view would avoid the awkward contradiction of exclamatory sentences constituting a special type and belonging to the first three types at the same time.