``Adjectives are coordinate if (1) they
can be linked by and and (2) they independently
modify the substantive''(Words Into Type).
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. The
comma adds emphasis though to the adjectives as separate
modifiers.
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 elliptical for the use of the
semicolon in elliptical constructions.
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 $10^20$ 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 10^20 may be required. In case of fire, the command
for stopping the test is ``Recover, fire.''
A comma that encloses requires a partner, which may be
another comma or a colon, semicolon, period, question
mark, or exclamation mark.
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
(see section introductory):
Restrictive - A random process is stationary if
for all n, its nth density function is
independent of time.
Nonrestrictive - The coefficient could be placed
elsewhere because, though preferred, the placement
shown is arbitrary.
Nonrestrictive relative clauses are enclosed with
commas:
Restrictive - The most common panel methods are
the codes which Hess and Smith (ref. 26) designed for
nonlifting bodies.
Nonrestrictive - 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 - The last chapter introduces
specialized areas where research is in progress.
Nonrestrictive - The power spectral density of
the signal is shown in figure 9, where arrows represent
delta functions.
Restrictive - Two random processes are
uncorrelated if their cross correlation satisfies
equation (6).
Nonrestrictive - 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 (see section introductory).
When an internal adverbial clause precedes the clause
that it modifies, do not place a comma before it unless it
is clearly nonrestrictive:
Wrong - Recombination rate is larger than
quenching rate, and, after lasing is achieved, both
are smaller than photo-break dissociation rate.
Correct - 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.
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 - The noble gas argon was
chosen for the lasant gas.
Nonrestrictive - 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 (section
dashenclose).
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 - The coefficients C_L and C_m
are plotted in figure 23.
Nonrestrictive - The lift coefficient C_L is
plotted in figure 23.
However, if the author or editor prefers,
nonrestrictive symbolic appositives may be enclosed by
commas:
The two most sensitive parameter in the estimations, is
compared with measured values in table II.
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 (see section 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.
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.
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.
The following conventional uses of the comma should be
considered enclosure rather than separation:
The study was conducted from January 15, 1975, to
February 1, 1979, aboard commercial airliners.
But
The study was conducted from January 1975 to February
1979 aboard commercial airliners.
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.
This conclusion was drawn from data in Volume II, page
157, of reference 16.
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.
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:
Correct - There were 88,000 data points, 2500 of
which had to be discarded.
Preferred - There were 88 000 data points, 2500
of which had to be discarded.
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
(see section parens).
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.
CONTINUED
