Punctuation : End Marks and Commas
Sentence End Marks
Definition: An end mark is a punctuation mark used at the end of a sentence to show that the sentence is finished. There are three end marks: the period, the question mark, and the exclamation mark.

Periods
Periods are used to end many types of sentences:

Declarative Sentences
The sun is shining this morning.
I want to go to the beach.
I can't find my keys.

Polite or Less Emphatic Imperative Sentences
Look under your chair.
Please be on time.

Indirect Questions
The teacher asked Michael why he was late.
Mom asked if you remembered to buy milk.

Question Marks
Question marks are used after interrogative sentences (direct questions). There are several types of interrogative sentences:

Basic Questions
Have you seen my other shoe?
Where have you been?

Question Fragments
I didn't eat the rest of the pizza, did you?
You are late. Why?

Imperative Sentences Phrased Like Questions
Would you please hand me that book?
Will you all please have a seat?

Exclamation Marks (also called Exclamation Points)
Exclamation marks are used to end several types of emphatic expressions:

Basic Exclamatory Sentences
I can't believe you won!
It's raining again!

Strong Interjections
Wow! That's a lot of money!
Whew! That was a close call.

Powerful Imperative Sentences
Watch out!
Be quiet!

Exclamations Phrased as Questions
What a beautiful home you have!
How wonderful!

Periods in Abbreviations
Definition: An abbreviation is a shortened form of a word. There are different kinds of abbreviations. Some use periods; others don't. Some are written in capital letters; others use lowercase letters. This is an area that is changing rapidly. It is always best to check a dictionary or a style manual to be certain.

People's Names and Titles
Abbreviations in people's names and titles generally do use periods, but academic degrees and Roman numerals do not require periods.

Periods

People's Names	People's Titles
John Q. Adams (Quincy) S. E. Hinton (Susan Eloise Hinton) (Also notice that there is a space after the first initial in the second example.)	Mr. (Mister) Mrs. (Missus, short for Mistress) Dr. (Doctor) Jr. (Junior) Sr. (Senior)

No Periods

Roman Numerals (after names of people or events)	Academic Degrees
John Parker III (pronounced John Parker the third, not John Parker three) World War II	BA (Bachelor of Arts) MA (Master of Arts) PhD (Doctor of Philosophy) RN (Registered Nurse)

Days and Months, Latin Phrases, Addresses Directions, and Traditional State vs. Postal State Abbreviations

Periods

Months	Jan.(January)
Days of the Week	Mon. (Monday) Tues. (Tuesday) Thurs. (Thursday)
Addresses	Ave.(Avenue) St. (Street)
Latin Phrases	i.e. (id est = in other words) e.g. (exempli gratia = for example) etc. (et cetera = and so forth)
Traditional State Abbreviations	Fla. (Florida) Mont. (Montana)

No Periods

Days of the Week: Two- or Three-Letter Abbreviations	Tu or Tue (Tuesday)
Directions (all caps)	NW(northwest) SE(southeast)
US Postal Abbreviations (all caps)	FL (Florida) MT (Montana)

Note: Three-letter abbreviations for days of the week can be written with or without a period at the end. Whether you decide to use periods or not, just remember to be consistent in your writing.

EXAMPLE
Tue. and Wed.
Tue and Wed

Measurements
Most measurements and scientific abbreviations do not use periods, but standard United States measurements and time abbreviations have a period at the end.

Periods

Standard US Measurements	in. (inch) ft. (foot) oz. (ounce)(The z in oz. comes from the Medieval Italian word onza.)
Time Abbreviations	sec. (second) h. or hr. (hour)

No Periods

Metric Measurements	ml (milliliter) km (kilometer) cg (centigram)
Math and Science	mph (miles per hour) mpg (miles per gallon) rpm (revolutions per minute)
Computer and Internet	CPU (central processing unit) URL (uniform resource locator) DVD (digital video disc)

Abbreviations in All Capitals
Abbreviations made up of the first letter of each word in a phrase, usually in all capitals, do not generally use periods, with some exceptions here and there.

Periods (Exception to the Above Rule)

The Abbreviation forDistrict of Columbia	Washington, D.C. (D.C. has periods even though it is pronounced letter by letter.)

No Periods (The Norm)

Acronyms	These are abbreviations pronounced as words instead of a string of letters. Some acronym abbreviations have actually become words themselves. NASA (National Aeronautics and Space Administration) NATO (North Atlantic Treaty Organization)
Abbreviations Pronounced Letter by Letter	FBI (Federal Bureau of Investigation) FYI (for your information) MVP (most valuable player)

Abbreviations that Can Go Either Way
Some abbreviations are rapidly changing. Either form is generally accepted, but check with your teacher or style manual to make sure.

Acceptable With or Without Periods
U.S.A. or USA
B.C., A.D., C.E., B.C.E. or BC, AD, CE, BCE (B.C. or BC: Before Christ; A.D. or AD: Anno Domini; C.E. or CE: Common Era; B.C.E. or BCE: Before Common Era)
a.m., p.m. or AM, PM If lowercase, use periods. If capitals, do not use periods. (a.m. or AM: ante meridiem/before midday; p.m. or PM: post meridiem/after midday)

Abbreviations and End Punctuation
If you end a sentence with an abbreviation containing a period, do not put another period at the end of the sentence. However, if a sentence ends in an exclamation mark or a question mark, include both the abbreviation's period and the end mark.

EXAMPLE
His son's name is Jason Miller Jr. (abbreviation period only, no end period)
Is his son's name Jason Miller Jr.? (abbreviation period + ending question mark)

Commas in a Series
Definition: A comma separates elements in a sentence, such as items in a list or series, but it also shows that those elements are connected to each other within the same sentence. A comma is never used as an end mark, and it is read with a shorter pause than an end mark. One use of the comma is to separate three or more words, phrases, or clauses in a list or series. Commas go after each item except the last.

Note:
In British usage, there is no comma before the conjunction (such as and or or) before the last item in the series.

Words in a Series
You need to get out your pencil, paper, and textbook.
I will need tomatoes, spinach, and cheese for this recipe.

Phrases in a Series
Next summer I want to go kayaking in the ocean, hiking in the Appalachian Mountains, and surfing in Florida.
The puppy chased the kitten under the sofa, around the kitchen chairs, and up the stairs.

Clsuses in a Series
We went to the mall, and we went to the movies, but we didn't go out to eat.
Misha wasn't sure if you were coming, you and Marcello were coming, or everyone was coming.

Note:
If conjunctions are used for emphasis to separate items in a series, commas are not used.

EXAMPLE
I felt like I had been poked and prodded and persecuted.

Commas with Adjectives
A series of adjectives that comes before a noun can be classified as coordinate or cumulative.

Coordinate Adjectives
Definition: Coordinate adjectives modify nouns in similar ways. They describe similar features. Most coordinate adjectives are adjectives of opinion or evaluation. Commas must be used between coordinate adjectives.

EXAMPLE
That frightening, monstrous creature under the bridge is a troll.

Cumulative Adjectives
Definition: Cumulative adjectives build upon each other and must be in a certain order. They are equally important and give different types of information. Do not use commas between cumulative adjectives.

EXAMPLE
Two tall pillars were used to form the entrance to Stonehenge.

Traditional Explanation
The way to figure out whether adjectives are coordinate or cumulative is to put the conjunction andbetween the adjectives or to see if they can be switched around. If the sentence still sounds natural when you add and or change the adjective order, add a comma.

Coordinate Adjectives
That frightening and monstrous creature under the bridge is a troll.	These sentences both sound fine, so you can tell that these are coordinate adjectives of opinion.
That monstrous, frightening creature under the bridge is a troll.

Cumulative Adjectives
Two and tall pillars were used to form the entrance to Stonehenge.	These sentences both sound awkward. Because you cannot add and or change the adjective order, you know that these are cumulative adjectives.
Tall two pillars were used to form the entrance to Stonehenge.

These sentences both sound awkward. Because you cannot add and or change the adjective order, you know that these are cumulative adjectives.

Add a Comma for Clarity
Sometimes a comma is inserted to clarify that two adjectives modify an adjective-noun combination.

EXAMPLE
The delicious, moist chocolate cake The chocolate cake is delicious and moist. Chocolate cake is the adjective-noun combination (chocolatetells us what kind of cake we're talking about). Delicious and moist are separate adjectives that describe chocolate cake.
The delicious moist chocolate cake The moist chocolate cake is delicious. The adjective delicious is modifying the whole phrase moist chocolate cake. The adjective moist has fused with chocolate cake.

Commas in Compound Sentences
A comma is generally used to separate two or more independent clauses in a compound sentencethat is joined by a coordinating or, occasionally, a correlative conjunction.

EXAMPLE
The children learned to ride their bicycles, and then they rode them in the park.
I want to see that new movie, but I am too late.
Sammi wants to get a new haircut, so we are going to the salon on Friday.

If you're not sure whether or not the sentence needs a comma, check to see if each half of the sentence makes sense by itself. You can test whether each half makes sense by replacing the conjunction with a period. If each half does make sense by itself, you need to add a comma before the conjunction. Compound subjects and compound predicates are not separated by commas.

EXAMPLE
I visited my sister in London and had a wonderful time.

This sentence doesn't need a comma because the second half of the sentence can't stand alone: had a wonderful time isn't a complete sentence because the subject is missing. This is an example of a compound predicate (visited my sister + had a wonderful time), which doesn't require a comma.

EXAMPLE
I meant to return that book to you but forgot it on the kitchen table.

Just like the previous sentence, this one doesn't need a comma because forgot it on the kitchen table is missing the subject and doesn't make sense by itself.

Commas in Complex Sentences
If a complex sentence begins with a dependent adverb clause, a comma is used to separate the two clauses.

EXAMPLE
Since we are already late, we don't have time to stop.
If you have found the page, please begin reading.

If a complex sentence begins with an independent clause, no comma is used between the clauses.

EXAMPLE
We don't have time to stop since we are already late.
Please begin reading if you have found the page.