The punctuation system presented in this paper has explanatory power insofar as it explains how good writers punctuate. The paper notes that good writers have learned, through reading, the differences among a hierarchy of marks and acquired a sense of independent clauses that allows them to use the hierarchy, along with a reader-sensitive notion of clarity, to punctuate single independent clauses and conjoined independent clauses according to their semantic intentions. Because it is principle-based (with four rules), the system in the paper tolerates variations according to the writer's semantic intent (meaning)--that is, according to her or his determination of the needs of clarity. The system presented accounts for both the early punctuation of Isak Dinesen, which shows a nonnative speaker unsure of the system, and her later works which show her in control of the system. The system also accounts for the style of James Joyce in "Dubliners" and for John Updike's conservative punctuation in nonfiction but liberal punctuation in fiction. The system presented in the paper focuses on what "good" writers do and suggests how others can do the same. By allowing options according to the need for clarity, the system encourages careful analysis and rewriting--what good writers have learned to do. Three tables representing aspects of the system of punctuation are included. (Contains 19 references.) (RS)