English Language: Commonly Confused Words

Which, That, and Who
Which is used for things only.
John's dog, which was called Max, is large and fierce.
That is used for people or things.
Example: Is this the only book that Louis L'Amour wrote?
Louis L'Amour the author that wrote Western novels?
Who is used for people only.
Example: Mozart was the composer who wrote those operas.

Homophones
Homophones are words that sound alike (or similar), but they have different spellings and definitions.

To, Too, and Two
To can be an adverb or a preposition for showing direction, purpose, and relationship. See your dictionary for the many other ways use to in a sentence.
Examples: I went to the store. | I want to go with you.

Too is an adverb that means also, as well, very, or more than enough. can walk a mile too. | You have eaten too much.
Two is the second number in the series of numbers (e.g., one (1), two, (2), three (3)…)

Example: You have two minutes left.

There, Their, and They're
There can be an adjective, adverb, or pronoun. Often, there is used to show a place or to start a sentence.
Examples: I went there yesterday. 

There is something in his pocket.
Their is a pronoun that is used to show ownership.
Examples: He is their father. 

This is their fourth apology this week.
They're is a contraction of they are.

Example: Did you know that they're in town?

Knew and New
Knew is the past tense of know.
Example: I knew the answer.
New is an adjective that means something is current, has not been used, or modern.

Example: This is my new phone.

Then and Than
Then is an adverb that indicates sequence or order:
Example: I'm going to run to the library and then come home.
Than is special-purpose word used only for comparisons:

Example: Susie likes chips better than candy.

Its and It's
Its is a pronoun that shows ownership.

Example: The guitar is in its case.
It's is a contraction of it is.

Example: It's an honor and a privilege to meet you.
Note: The h in honor is silent, so the sound of the vowel o must have the article an.

Your and You're
Your is a pronoun that
This is your moment to shine.
You're is a contraction of you are.

Example: Yes, you're correct.

Affect and Effect
There are two main reasons that affect and effect are so often confused: 1) both words can be used as either a noun or a verb, and 2) unlike most homophones, their usage and meanings are closely related to each other. Here is a quick rundown of the four usage options:
Affect (n): feeling, emotion, or mood that is displayed
Example: The patient had a flat affect. (i.e., his face showed little or no emotion)
Affect (v): to alter, to change, to influence sunshine affects the plant's growth.
Effect (n): a result, a consequence
What effect will this weather have on our schedule?
Effect (v): to bring about, to cause to be
Example: These new rules will effect order in the office.

The noun form of affect is rarely used outside of technical medical descriptions, so if a noun form is needed on the test, you can safely select effect. The verb form of effect is not as rare as the noun form of affect, but it's still not all that likely to show up on your test. If you need a verb and you can't decide which to use based on the definitions, choosing affect is your best bet.

Homographs
Homographs are words that share the same spelling, and they have multiple meanings. To figure out which meaning is being used, you should be looking for context clues. The context clues give hints to the meaning of the word. For example, the word spot has many meanings. It can mean 'a place' or 'a stain or blot.' In the sentence 'After my lunch, I saw a spot on my shirt,' the word spot means 'a stain or blot.' The context clues of 'After my lunch…' and 'on my shirt' guide you to this decision.

Bank
(noun): an establishment where money is held for savings or lending
(verb): to collect or pile up

Content
(noun): the topics that will be addressed within a book
(adjective): pleased or satisfied

Fine
(noun): an amount of money that acts a penalty for an offense
(adjective): very small or thin

Incense
(noun): a material that is burned in religious settings and makes a pleasant aroma
(verb): to frustrate or anger

Lead
(noun): the first or highest position
(verb): to direct a person or group of followers

Object
(noun): a lifeless item that can be held and observed
(verb): to disagree

Produce
(noun): fruits and vegetables
(verb): to make or create something

Refuse
(noun): garbage or debris that has been thrown away
(verb): to not allow

Subject
(noun): an area of study
(verb): to force or subdue

Tear
(noun): a fluid secreted by the eyes
(verb): to separate or pull apart