Defining "sentence" may be a difficult problem for linguists, but recognizing a sentence is as simple as recognizing a single potato in a sack of potatoes. A sentence is a group of words beginning with a capital letter and ending with a period. Sometimes the period is replaced by a question mark or exclamation mark. That's it.

The punctuation code has evolved over the course of centuries and to some extent is still evolving. It is a difficult code to learn, it is managed largely by editors, and writers often personalize their use of the code. The choice and placement of punctuation marks are meaningful to writers and editors and, they hope, to readers. Regardless of the firm rules that editors follow from their style books, punctuation is to an important degree subjective and can be controlled by the writer's predilections. He can use punctuation to convey a variety of meanings, often so subtle that only an alert reader with practice reading that author will be aware of them. But even the reader's awareness of the writer's personal code for semi-colons, say, does not ensure correct interpretation of the writer's meaning. Punctuation is an extremely loose code; it is hard to break.

Lewis Mumford, author of several weighty dissertations on machines and cities, made the colon a distinctive part of his style. The colon, probably the least popular mark of sentence punctuation, is used ordinarily in sentences in which a complete statement announces an important piece of information that follows the colon: an emphatic completion of the sentence, customarily a noun phrase like this one. The authoritative University of Chicago Press Manual of Style   points out that the colon is used "to mark a discontinuity of grammatical construction greater than that indicated by the semi-colon and less than that indicated by the period." Mumford reinforces his declaratory style often by using the colon. You need read only half a page to find one. He likes to announce his ideas, but he uses the colon in other ways as well. I choose at random a passage from The City in History  (p. 284):

But there is still a brewery in Bruges which now occupies almost one whole side of Walplaats, built on the same scale as the residence beside it: the loading is done in the courtyard behind.

At first glance, the colon is puzzling. Why doesn't Mumford use a period? A more alert reading of the page told me. The preceding sentence provides the context:

The competition for space between the domestic and the working quarters, as business grew and the scale of production expanded, was doubtless responsible for encroachment over the original back gardens by sheds, storage bins, and special workshops.

It's clear now that the colon subtly links the apparently incidental comment about loading to the idea in the preceding sentence about the competition between domestic and working quarters and that loading is encroaching over the courtyard. Not an incidental comment to be punctuated as a separate sentence. I accept Mumford's sentence as one complete thought as punctuated. I must disagree with the implication of the editors of the University of Chicago Press that the semi-colon suggests a closer link between two grammatical elements than does a colon. A semi- colon instead of a colon in Mumford's sentence would suggest a greater discontinuity than would a colon. I leave you to ponder the extremely colonic structure of the following sentence from Mumford's The Myth of the Machine  (p. 66):

What Huizinga says of play is basic to man's early expression in ritual: ritual creates order and is order: indeed, it is probably the aboriginal form of that make-believe which is inseparable from human culture: the game, the drama, the ceremony, the contest, in fact the whole range of the symbolic performances.

Three colons in one sentence! And, according to my definition, it is still one single sentence.

E-mail and comments to:   Arnold Nelson

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