Usage

Language changes.  The differences between many of these pairs of words are not nearly as distinct as I imply.   Still, wouldn't you rather be thought of as obsessively correct than egregiously wrong?  

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

accept/except
Accept means to agree to.  
Except means to leave out. Notice that prefix, ex.  Think of the other words you know that contain it.  exit, extraneous, etc. Does it make it easier to remember the meaning?

Advise/advice
advise is the verb.  Advice is the noun.  I advise you not to give advice.

Affect/effect.  The word affect is usually a verb; the word effect is usually a noun. 
One way to remember the difference is to think of the word VANE:  V (verb) A (affect) N (noun) E (effect).

all ready & already
They are both correct, but have different meanings.
We are all ready to go to the movie.  I have already finished my work. 

all right & alright
Alright is ALL WRONG.

altogether and all together
I had twenty dollars altogether. (all told)
Let us go all together to the movies. 

allusion & illusion
I made an allusion to my novel. 
My belief that I'd written a novel was merely an illusion.  I've written nothing.  

Alter/altar
Alter is a verb that means to change.  Altar is a noun meaning the center table or place for worship.

Anxious/eager
If you'd love to go to the concert, you're eager to go.  If you're anxious about going, you have some anxieties about the matter.

B
bring/take
It's all in your point of view.  

C
Celibate/chaste
A celibate person is unmarried and presumably doing without sex--by choice.  
A chaste person is not having illicit sex. (A married woman could be chaste--while enjoying sex with her husband.)

compare to & compare with
You compare one thing to another when you find them similar. "Shall I compare thee to a summer day?"
You compare one thing with another to find the similarities and differences.  

complement & compliment
You compliment your friend on his new haircut. I like it.
One thing complements another when the two make up a satisfying whole.

continual & continuous
Continuous torment in hell would be worse than continual torment, because continuous means without interruption, continual means occurring over and over again.

D
Decimate
The word originally meant to kill one tenth of the number.  Don't use it to mean destroy all; use it to mean to do widespread destruction.

disinterested & uninterested
A disinterested juror is impartial; an uninterested juror couldn't care less.

E
Elicit/illicit
By your abiding faith in him, you elicit his strengths. (bring out)
Unfortunately for law-abiding people, his strengths are all illicit activities.  We expect him to be arrested anytime.

eminent & imminent
An eminent person is famous.
But that thunderstorm is imminent: better get inside fast.

extrapolate & interpolate
We'll extrapolate this data to another situation.  (go beyond the data)
The fool interpolated his words into Shakespeare's sonnet and thought we'd never know the difference:  "Shall I compare and contrast thee to a beautiful July summer's day?"


Famous, infamous, notorious
Famous means well-known.  Infamous and notorious both mean famous in a negative way.

farther & further
I try to walk farther each day.  (distance)
If you study hard, you will go further in your careers than others. (At least, that's what they tell us.)

flotsam and jetsam.
Flotsam is the wreckage after a shipwreck; jetsam is the stuff thrown overboard in hopes that the ship doesn't founder.  Both may be floating afterwards.

fewer/less
Fewer refers to a number, to countable items.  I took fewer courses than you last term.
Less refers to an amount, to noncountable nouns.  You had less time than I.

figuratively & literally
She was always a melodramatic person.  She announced one day that she would literally die if the professor called on her. (Surely she meant figuratively die--but that didn't sound as good.)  He called on her soon after.  It turned out that she was literally right--and was pronounced dead on the spot.

first & firstly
Use first, second...tenth.  (NOT firstly, secondly, tenthly).

flammable & inflammable
Both mean the same thing.  Those oily rags are flammable (inflammable).

G

H
hanged & hung
The clothes were hung on the line.  But the prisoner was hanged by the neck until he was dead.

I
imply & infer
While I was talking to you, I implied that I was wealthy.
You inferred from my speech that I was delusional.

irregardless
Not a word.  Use regardless

its/it's.  
The apostrophe in it's take the place of the missing letter "i."  It's cold today.
Its, the possessive form of it, has no apostrophe.  Neither does his, her, my, or any other possessive pronoun.

J

K

know/no
The spell checker is a wonderful thing, but it won't catch mistakes like this.  Proof read to catch errors with homonyms.  

L

lay/lie
lay is a transitive verb; that is, it takes an object.
The hen lays eggs.  Lay the book on the table.
lie is an intransitive verb.
Lie down and rest.  

But another problem arises when you use the verbs in the past tense. 
The past tense of lay is laid; the past tense of lie is lay.
Yesterday, the hen laid two eggs.
Yesterday, he lay down for an hour.

lead/led 

M

N

O

P
percent & percentage
Use percent with numbers: ten percent
Use percentage with amounts.  A large percentage.

principal & principle
We all remember that "The principal is our pal. "  Don't forget that the more general meaning of principal is "main," as in The principal reason for the failure of this product.... 
Principle means rule.  Notice both end in "le."

Q
Quote/quotation marks/quotation
Quote is the verb.  Don't quote me.
Quotation marks are the squiggly marks.  Put quotation marks around the quotation.(NOT quotes around the quote)
Quotation is the noun. Use many quotations in your paper.  (NOT quotes in your paper)

R
This is when...The reason is because...Incorrect constructions.  The linking verb "is" should be followed by a noun or adjective.

S
Sea change
Not any kind of change.  A change into something rich and strange. From Shakespeare's The Tempest.

Full fathom five thy father lies:
Of his bones are coral made:
Those are pearls that were his eyes:
Nothing of him that doth fade
But doth suffer a sea-change
Into something rich and strange.

sensual & sensuous
Both are related to the senses.
That gross lewd person takes sensual pleasure in some unsavory activities your mother wouldn't approve of.
You, however, have a sensuous delight in classical music.

shall/will.  Click for explanation.

should have/should of.
The students should have studied longer for their exam. 
(Should of is not correct.)

stationery/stationary
Stationary means standing still.  Notice the "a" in stationary and stand.
Stationery means letters, envelopes, etc.  Notice the "e" in all those words.

T

their/there/they're

  • There answers the question whereWhere did he put the book?  There, on the desk. Notice both words end in "ere."

  • The apostrophe in they're signals the omission of a letter, the letter "a." They're too tired to study.

  • Their is the possessive pronoun.  Their dinner, their books, their time.

toward & towards
Use toward.

U
Ultimate, penultimate, antepenultimate
The ultimate is the last.  The penultimate is the one before that.  The antepenultimate is the one before the one before the last.  
The antepenultimate syllable is often stressed in English.  beau-ti-ful.

use & utilize
Why in the world would you use a long, stuffy word like utilize when you know a perfectly good word like use?

V

W

where/were
Where are the books?  
They were in the store. They were going.  [Were is the past tense, plural of the verb to be. It's often used as an auxiliary verb.]  

X

Y

Z