ENGLISH LANGUAGE PUNCTUATION MARKS

Comma

5. English Language Punctuation - Comma

Of all the marks of punctuation, the comma requires the most judgment. To punctuate with commas requires not only compliance with a set of rules but also thorough understanding of the material being punctuated. Commas can change meaning! The primary functions of the comma are to separate and to enclose elements of a sentence. The function of a particular comma is important: when it separates, it stands alone, but when it encloses, it needs a partner. The instances when commas separate sentence elements are discussed first in this section, and then the instances when commas enclose.

5. a) English Language Punctuation - Commas That Separate

Many separating uses of the comma are optional in an open style. If commas are used whenever possible, they chop up the text and can even render it difficult to read, contrary to the purpose of punctuation. Independent clauses Independent clauses joined by coordinate conjunctions may be separated by a comma: The mixing noise dominates the spectrum, but the background noise peaks at a high frequency. When the independent clauses are short and closely related, the comma may be omitted: Each performance of an experiment is called a trial and its result is called an outcome. The comma is usually retained between clauses joined by the coordinate conjunctions but and for, in order to emphasize the contrast. When the independent clauses are complicated and contain internal commas, a semicolon may be used to separate them. Do not use a comma to separate independent clauses without a coordinate conjunction:

Wrong Either Or The differences were generally about 11 percent, however, larger differences occurred at = 15 °. The differences were generally about 11 percent, but larger differences occurred at = 15 °. The differences were generally about 11 percent; however, larger differences occurred at = 15 °.

Do not separate compound predicates with a comma unless they are long and require a comma for clarity. Poor Viewing through the atmosphere increases the apparent reflectance for low-reflectance objects (e.g., p = 0.1), and decreases the apparent reflectance for high-reflectance objects (e.g., p = 0.7). Viewing through the atmosphere increases the apparent reflectance for low-reflectance objects (e.g., p = 0.1) and decreases the apparent reflectance for high-reflectance objects (e.g., p = 0.7).


Correct

When compound predicates are so long that a comma seems appropriate, they are perhaps too long. A comma to separate them may not sufficiently clarify them. Elements of series Commas (at least) are required to separate series of three or more elements: The flight navigation system also provides altitude, roll, pitch, yaw, and ground speed. Pressures at the bulkhead, in the cove, and at the seal were measured. Wind speed is obtained from antenna brightness temperature, rain rate is obtained from the brightness temperature difference at two frequencies, and wind vector is obtained from radar cross section. We prefer a comma before the conjunction in a series. This serial comma is often necessary to prevent misreading. Introductory phrases and clauses A comma may be used to separate an introductory phrase or clause from the main clause: If the variable t is actually time, then a is frequency. One has considerable freedom in defining the Fourier transform pair. It is standard practice to put the comma after all introductory clauses and all introductory phrases containing a verb form (Ebbitt and Ebbitt 1982):

Clause Participal phrase Gerund phrase Infinitive phrase Although some mathematicians are not comfortable with this intuitive definition, it is widely used. Called mean square calculus, this theory is based on the concept of mean square convergence. In analyzing the experiment, we try to statistically describe the whole random process. To understand this concept, note that periodic functions may be expanded in Fourier series.

The comma is optional after a short introductory adverbial phrase unless the comma is required for clarity: Either Or Wrong Better In recent years, the delta function has been rigorously defined. In recent years the delta function has been rigorously defined. Soon after the photon density becomes steady as gains and losses balance each other. Soon after, the photon density becomes steady as gains and losses balance each other.

Do not place a comma after an introductory phrase that immediately precedes the verb it modifies: Wrong Correct Only in recent years, has the delta function been rigorously defined. Only in recent years has the delta function been rigorously defined.

Remember that after introductory clauses and phrases the comma is separating, not enclosing. A comma is appropriate after an internal phrase or clause, but it is not appropriate before unless the phrase or clause is nonrestrictive. A comma follows, but does not precede, restrictive introductory elements: Wrong Correct Wrong Correct Recombination rate is larger than quenching rate, and, after lasing is achieved, both are smaller than photo-break dissociation rate. Recombination rate is larger than quenching rate, and after lasing is achieved, both are smaller than photo-break dissociation rate. The laser pulse was reasonably stationary, although, at 1.6 msec, motion of the arc is evident. The laser pulse was reasonably stationary, although at 1.6 msec,motion of the arc is evident.

A comma both precedes and follows nonrestrictive introductory elements:

Correct Note that, even though they are unbounded, the delta functions are plotted as arrows with their heights representing the coefficient magnitudes.

Coordinate adjectives "Adjectives are coordinate if (a) they can be linked by and and (b) they independently modify the substantive" (Linton 1962). Separate by commas only those consecutive adjectives that are coordinate. Deciding whether adjectives are coordinate can be tricky; two tests might help. First try inserting and between the adjectives: The delta function has a long controversial history. (long and controversial?) A comma is appropriate between long and controversial. Consider a linear shift-invariant system. (linear and shift-invariant?) If still in doubt, try reversing the adjectives (if they independently modify the noun, order makes no difference): Consider a shift-invariant linear system. The adjectives shift-invariant and linear are probably coordinate, but the final decision requires someone who understands the technical meaning of the adjectives. (Good luck with trying to explain this grammatical dilemma!) When in doubt, do not insert the comma between adjectives. The current tendency is to omit the comma between two coordinate adjectives anyway (Ebbitt and Ebbitt 1982). The comma adds emphasis though to the adjectives as separate modifiers. Elliptical constructions When clauses in a sentence contain repeated elements (for example, the verb), the omission of these elements is indicated by a comma: Wind speed is obtained from antenna brightness temperature; rain rate, from the brightness temperature difference at two frequencies; and wind vector, from radar cross section. The comma may be omitted if the clauses are short: Wind speed is obtained from antenna brightness temperature, and wind vector from radar cross section. Note: See section 15.4 for the use of the semicolon in elliptical constructions. Direct quotations and questions Direct quotations and questions are separated from the rest of the sentence with either commas or colons. A colon is used to introduce a long or formal quotation. Separate a direct quotation or question from the rest of the sentence with a comma: In reference 6, he states, "Thermal neutron fluxes up to 1020 might be required." The obvious question is, how good is this estimate?

Note: The first word of the question may or may not be capitalized.

Neither a comma nor a colon sets off an indirect quotation or one that is part of the grammatical structure of the sentence: In reference 6, he stated that thermal neutron fluxes up to 1020 may be required. In case of fire, the command for stopping the test is "Recover, fire."

5. b) English Language Punctuation - Commas That Enclose

A comma that encloses requires a partner, which may be another comma or a colon, semicolon, period, question mark, or exclamation mark. Nonrestrictive modifiers A nonrestrictive modifier does not affect the meaning of the basic sentence; it could be removed from the sentence without altering meaning. Nonrestrictive modifiers must be enclosed by commas (at least). The important point to remember is that an enclosing comma requires a partner, which can be another comma or another mark of punctuation. The nonrestrictive prepositional and verbal phrases are enclosed with commas in the following examples: The record need not be continuous but may, in fact, be digital data. Theoreticians prefer to work in terms of radian frequency, defined for both positive and negative frequencies. The power spectral density is integrated over some finite bandwidth, such as a one-third octave. The second integral, being the integral of an odd function over even limits,is zero. Be sure to distinguish between restrictive and nonrestrictive internal phrases that introduce clauses: Restrictive Nonrestrictive A random process is stationary if for all n, its nth density function is independent of time. The coefficient could be placed elsewhere because, though preferred, the placement shown is arbitrary.

Nonrestrictive relative clauses are enclosed with commas: Restrictive Nonrestrictive The most common panel methods are the codes which Hess and Smith (ref. 26) designed for nonlifting bodies. The most common panel methods are the codes of Hess and Smith (ref. 26), which were developed for nonlifting bodies.

Nonrestrictive adverbial clauses are enclosed with commas: Restrictive Nonrestrictive Restrictive Nonrestrictive The last chapter introduces specialized areas where research is in progress. The power spectral density of the signal is shown in figure 9, where arrows represent delta functions. Two random processes are uncorrelated if their cross correlation satisfies equation (6). Independent random processes are uncorrelated, since their cross correlation always satisfies equation (6).

Whether restrictive or nonrestrictive, an introductory adverbial clause is separated by a comma from the clause it modifies. When an internal adverbial clause precedes the clause that it modifies, do not place a comma before it unless it is clearly nonrestrictive: Wrong Correct Recombination rate is larger than quenching rate, and, after lasing is achieved, both are smaller than photo-break dissociation rate. Recombination rate is larger than quenching rate, and after lasing is achieved, both are smaller than photo-break dissociation rate.

The following guidelines, taken from Rowland, might be helpful in determining whether the clause is restrictive or nonrestrictive. Adverbial clauses can be categorized as follows: Time clauses-introduced by when, whenever, after, as soon as, just as, before, since, until, while-are restrictive when they modify the main verb. Place clauses-introduced by after, before, where, wherever-are usually restrictive, but may be nonrestrictive. Manner clauses-introduced by how, just as, as, as if, as though-are usually restrictive. Comparison or degree clauses-introduced by else, other, rather, as, than-are usually restrictive. Condition clauses-introduced by if, as though, except, provided, unless, whether-are usually restrictive. Concession clauses-introduced by although, even, while, whereas, though-are always nonrestrictive. Cause or reason clauses introduced by because are usually restrictive, but those introduced by since, as, inasmuch as are usually nonrestrictive. Purpose clauses-introduced by so that, in order that-are restrictive. Result clauses-introduced by so that-are nonrestrictive. Appositives Words or phrases in apposition are enclosed by commas unless the appositive is restrictive. A restrictive appositive is required to distinguish its antecedent from other members of the same class: Restrictive Nonrestrictive The noble gas argon was chosen for the lasant gas. Argon, the lightest noble gas that will lase, was chosen for the lasant gas.

Dashes (em) may enclose appositives to improve clarity, particularly when the appositive contains commas. The word or often precedes nonrestrictive appositives. The appositional or always requires enclosure: The concept of a laser powered directly by nuclear energy, or a direct nuclear-pumped laser, came into existence shortly after discovery of the laser. Commas are usually omitted around symbolic appositives, whether restrictive or not: Restrictive Nonrestrictive The coefficients CL and Cm are plotted in figure 2 The lift coefficient CL is plotted in figure 2

However, if the author or editor prefers, nonrestrictive symbolic appositives may be enclosed by commas: The two most sensitive parameters in the estimations, Interrupting elements Parenthetical phrases, rhetorical adverbs, antithetical phrases, introductory words, and other interruptive sentence elements may be enclosed by commas when they are nonrestrictive: Parenthetical phrase Auxiliary meteorological data used herein, such as vorticity, have been computed from NMC isobaric height fields. Rhetorical adverb The time between independent measurements cannot be reliably estimated; it can be assumed, however, to lie between 20 and 120 minutes.

Note: The placement and punctuation of rhetorical adverbs affect emphasis. Antithetical elements In winter, clouds near the tropopause are associated with negative vorticity, not with positive vorticity as most meteorologists are accustomed to believing. Interruptive words or phrases For 33-mm-diameter particles, for example, partial loss of laminar flow is predicted for large number densities. Phrases with common termination Enclose by commas a phrase with termination that also reads back to a previous phrase: An aircraft flying through clouds will lose a significant portion, if not all, of its laminar flow. The particle-concentration data have nearly the same latitudinal, but a significantly different seasonal, distribution from that of the cloud-encounter data. and are compared with measured values in table II.

Nominative absolute A nominative absolute phrase (that is, a noun with no grammatical function in the sentence modified by a participle) is nonrestrictive and thus is enclosed by commas: Most confidence may be placed in the statistics for the 30 deg N to 60 deg N latitude band, more data having been taken at these latitudes.

5. c) English Language Punctuation - Conventional Uses of the Comma

The following conventional uses of the comma should be considered enclosure rather than separation: Dates

But

The study was conducted from January 15, 1975, to February 1, 1979, aboard commercial airliners. The study was conducted from January 1975 to February 1979 aboard commercial airliners.

Geographical names and addresses These instruments were carried on commercial airliners en route from Chicago, Illinois, to London, England. The computer program is available from COSMIC, 112 Barrow Hall, University of Georgia, Athens, GA 30602. English Language Punctuation - Specifying phrases This conclusion was drawn from data in Volume II, page 157, of reference 16. English Language Punctuation - Degrees, titles, affiliations, etc. Members of the committee consisted of J. J. Deluisi, Ph.D., NOAA Environmental Research Laboratory; J. P. Friend III, Drexel University; and M. P. McCormick, chairman, NASA Langley Research Center. Names Refer to the report by J. J. Deluisi, Jr., and James P. Friend III: Deluisi, J. J., Jr.; and Friend, James P., III: Listing of Multi-Spectral dots The comma is used by convention to separate thousands in numbers of five or more digits; but in technical work, we prefer a (thin) space over a comma because in some foreign languages the comma indicates the decimal point: Numbers

Correct Preferred There were 88,000 data points, 2500 of which had to be discarded. There were 88 000 data points, 2500 of which had to be discarded.

5. d) English Language Punctuation - Use With Other Marks

Commas are used with other marks of punctuation as follows: Commas precede closing quotation marks. Commas follow a closing parenthesis if the comma would appear without the parenthetical matter. Commas rarely precede an open parenthesis, only if the parenthetical matter clearly limits the following word. Other marks of punctuation--semicolon, colon, dash, period--supercede and replace the comma; thus, the "partner" of an enclosing comma may be another mark of punctuation.