Common Usage Mistakes

Accept: to receive something (I accepted the gift he offered me.)
Except: excluding something (Everyone except Mark got on the boat.)

Advice: opinion or information offered; a noun (She offered her advice.)
Advise: to offer advice to someone; a verb (The senate members advised the president.)

Affect: to influence; a verb (The pungent odor affected me, making my eyes water.)
Effect: result; a noun (The presentation had a powerful effect on the country.)

All ready: used as an adjective to express complete preparedness (I was all ready to go.)
Already: an adverb expressing time (Unfortunately, everyone had already left.)

All right: correct use
Alright: incorrect use

Awhile: an adverb (Stay awhile.)
A while: an article and noun (Stay for a while.)

Can: denotes ability (I can touch my toes.)
May: denotes permission (May I sit here?)

Complement: complete, accentuate (His cummerbund complemented her dress color.)
Compliment:  to give praise (He complimented me on my paper grade.)

Conscious: awake or perceiving; an adjective (Despite a head injury, he was conscious.)
Conscience: the voice in the back of your head; a noun (Chris didn’t cheat because his conscience wouldn't let him.)

Everyday: something ordinary or common; an adjective (Those are my everyday shoes.)
Every day: used when something happens every single day (I clean my room every day.)

Good: describes nouns (That cake was really good.)
Well: describes verbs (She swims really well.)

Lead: either a noun (pronounced “led”), as in “the lead in the pencil,” or a verb (pronounced “leed”), as in “lead me to your ruler.”
Led: the past tense form of lead (I led the horse to water.)

Lose: to misplace something, a verb (Don’t give the money to her; she’ll lose it.)
Loose: the opposite of tight, an adjective (My shoelaces are loose.)

Principal: the head of a school (Mr. Belden was the principal on Saved by the Bell.)
Principle: a theory or belief (The professor explained Descartes principles to us.)

Then: used for a sequence of events or the passage of time (I went home, then slept.)
Than: used in comparison (I’m heavier than she is.)

To: a preposition (Take that book to her.)
Too: used when there’s too much, too many, too little of something (I grabbed for her, but she fell too fast.)
Two: the number (My daughter is two.)

We’re: contraction for we are (We're glad to help.)
Where: location (Where are you going?)
Were: a past tense form of the verb be (They were walking side by side.)