Punctuation is from the Latin, “pungere,” meaning “to prick,” “pierce,” “poke” or “punch.” It comes from an Indo-European root, *peuk, meaning, to “pierce,” “prick,” “poke” or, “punch.” Thus, in Grammar it is some sort of pointed mark in Speech demonstrating a pause, break, or end of some sort; or drawing attention to, or marking something in what is spoken. Most of us will, no doubt, think of the visual signs of full stop and exclamation marks and the rest as comprising Punctuation. But these are only visual representations of sounds or lack of them in spoken Speech. The overall purpose of punctuation, whether spoken or written, is to add meaning to Speech by demonstrating to the listener or reader certain stylistic or grammatical points. The sentence is an idea or thought. At the end of the idea or thought comes a pause however small before another idea or thought. In spoken Speech, the pause, after an idea, is heard, or rather, not heard. In written Speech this end is represented by a “full stop” mark.
Some consider degree of pause starting wth a comma, as the briefest or least final of pauses with semi-colon, colon and full stop following in order of degree of finality. But upon consideration of comma as the end of a clause, and a sentence may be a single clause, while a semi-colon and colon are interuptions within a clause, the degree of greater finality would surely rest with the comma. Length and “strength” of pause may be thought the measure but, again, many sentences can be joined together quickly, while pauses after colons, for example, can be “heavy” and long.
Beside degrees of final pauses, written Punctuation includes visual marks that clarify where certain phenomena begin or end, clear in spoken Speech but not in written Speech. Quotation marks are an example.