The word punctuation is derived from the Latin punctus, "a point." It refers to the system of marks or points inserted in a text to clarify the meaning or signal a change in pitch or intonation. Ancient Greek grammarians used only three points, placed high, low, or at midline, to indicate grammatical units and subunits. Hebrew scribes marked vowel signs and accents above or below the lines of the Masorah, or sacred text. Medieval English scribes differed in their practice but commonly used a medial point, a semicolon, an inverted semicolon (called a punctus elevatus), and a virgule. William Caxton, the first English printer, used only a virgule, comma, and period.
Modern punctuation is, by contrast, complex. Some punctuation marks divide discourse according to a scale of grammatical relationships. The period (.) indicates completion of the largest punctuated unit, the sentence; next in rank, the colon (:) indicates major divisions within a sentence. In descending order follow the semicolon (;), which marks off minor sentence divisions; the comma (,), marking off groups of word units; and, finally, the apostrophe ('), denoting possession, either singular as in John's coat or plural as in the two girls' coats. Other punctuation marks indicate the pauses, stresses, and changes of pitch in live speech. The interrogation point, or question mark (?), signals a question; the exclamation point (!) indicates emphasis; the dash (--) marks a break in the sentence; the hyphen (-) separates words or word elements, as in vice-president; ellipsis points (. . .) signify an omission; and quotation marks (" ") encompass the words of a speaker. Parentheses () set off incidental explanatory material, and square brackets enclose editorial interpolations.
Bibliography: Drake, W. D., The Way to Punctuate (1971); Follett, Wilson, Modern American Usage, ed. by Jacques Barzun (1966); Skillin, Marjorie E., et al., Words into Type, 3d rev. ed. (1986); University of Chicago Press, A Manual of Style, 13th ed. (1982)