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The colon is used by convention as follows:
After the salutation in formal letters: Dear Sir:
Between hours and minutes in time: 11:30 a.m.
In reference citations: Slater, Philip N.: Remote Sensing . . .
To express ratios: 2:1 mixture
3.4.3. Use With Other Marks
A colon follows closing parentheses and closing quotation marks.
3.5. 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.
3.5.1. 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 (see section 1.8.1) 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:
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Chapter 3. Punctuation
Wrong The differences were generally about 11 percent, however,
larger differences occurred at = 15 °.
Either The differences were generally about 11 percent, but larger
differences occurred at = 15 °.
Or 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).
Correct 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).
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.
As discussed in reference 4, 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):
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Chapter 3. Punctuation
Clause Although some mathematicians are not comfortable with
this intuitive definition, it is widely used.
Participal phrase Called mean square calculus, this theory is based on the
concept of mean square convergence.
Gerund phrase In analyzing the experiment, we try to statistically describe
the whole random process.
Infinitive phrase 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 In recent years, the delta function has been rigorously
defined.
Or In recent years the delta function has been rigorously
defined.
Wrong Soon after the photon density becomes steady as gains and
losses balance each other.
Better 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 Only in recent years, has the delta function been rigorously
defined.
Correct 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 (see section commasenclose).
" A comma follows, but does not precede, restrictive introductory elements:
Wrong Recombination rate is larger than quenching rate, and, after
lasing is achieved, both are smaller than photo-break
dissociation rate. [ Pobierz całość w formacie PDF ]