Sentences are of two kinds, simple and compound.
A simple sentence has in it but one subject and one finite verb; that is, a verb to which number and person belong: as, “A joke is a joke.”
A compound sentence consists of two or more simple sentences connected together: as, “A joke is a joke, but a ducking is no joke. Corpulence is the attribute of swine, mayors, and oxen.”
Simple sentences may be divided (if we choose to take the trouble) into the Explicative or explaining; the Interrogative, or asking; the Imperative, or commanding.
An explicative sentence is, in other words, a direct assertion: as, “Sir, you are impertinent.”—Johnson.
An interrogative sentence “merely asks a question:” as, “Are you a policeman? How’s your Inspector?”
“How’s your Inspector?”
An imperative sentence is expressive of command, exhortation, or entreaty: as, “Shoulder arms!” “Turn out your toes!” “Charge bayonets!”