McDonald, P. B. (1946). The difficult art of punctuation. In P. B. McDonald, Personality and English in technical personnel (pp. 191-200). New York, NY, US: D Van Nostrand Company.
http://dx.doi.org/10.1037/14621-019
Punctuation is a test of a finished writer's ability. Although seemingly trivial, it is very important. Many people punctuate thoughtlessly; relatively few punctuate correctly. A comma misplaced or omitted may change the whole meaning of a sentence. A semicolon wrongly inserted in the middle of a clause or where only a comma should be used, stamps a writer as either ignorant or scatter-brained. A superfluity of ink spattered over la page in unnecessary quotation marks, capitals, parentheses, or dashes indicates a fumbling novice. Perhaps the most severe test of understanding of punctuation is the use of commas with non-restrictive clauses, and the proper omission bf commas with restrictive clauses. If a writer shows that he recognizes a restrictive clause when he sees one, there is hope for him. He shows such recognition by omitting commas and preferring that to which or who. Another mark of a finished writer is the ability to compose clear sentences, some of them fairly long, using little punctuation, or at least using only a moderate amount of it. Punctuation should be used sparingly but effectively. Its primary purpose is to make written matter clear to a reader. It accomplishes in writing what pauses and variations of expression in the voice accomplish in spoken language. The technical man should be especially careful in his use of punctuation. (PsycINFO Database Record (c) 2016 APA, all rights reserved)