Among/Between Among expresses a collective or loose relationship of several items: Chester found a letter hidden among the papers on the desk. Between expresses the relationship of one thing to another thing or to many other things: Posey spent all day carrying messages between Chester and the other students. The idea that between can be used only when talking about two things is a myth it’s perfectly correct to use between if you are talking about multiple binary relationships.
Assure/Ensure/Insure Assure means to tell someone that something will definitely happen or is definitely true: Posey assured Chester that no one would cheat at Bingo. Ensure means to guarantee or make sure of something: Posey took steps to ensure that no one cheated at Bingo. Insure means to take out an insurance policy: Posey was glad the Bingo hall was insured against damage caused by rowdy Bingo players.
Capital/Capitol Capital has several meanings. It can refer to an uppercase letter, money, or a city where a seat of government is located: Chester visited Brasίlia, the capital of Brazil. Capitol means the building where a legislature meets: Posey visited the cafe in the basement of the capitol after watching a bill become a law.
Defence/Defense Defense is standard in American English. Defence is found mainly in British English.
Empathy/Sympathy Empathy is the ability to understand another person’s perspective or feelings. Sympathy is a feeling of sorrow for someone else’s suffering. A sympathizer is someone who agrees with a particular ideal or cause.
Farther/Further Farther refers to physical distance: Posey can run farther than Chester. Further refers to metaphorical distance: Chester is further away from finishing his project than Posey is.
Historic/Historical Historic means famous, important, and influential: Chester visited the beach in Kitty Hawk where the Wright brothers made their historic first airplane flight. Historical means related to history: Posey donned a historical bonnet for the renaissance fair.
Principal/Principle Principal can be a noun or adjective. As a noun, it refers to the person in charge of a school or organization: Posey was called into the principal’s office. As an adjective, it means most important: The principal reason for this meeting is to brainstorm ideas for the theme of Chester’s birthday party. A principle (always a noun) is a firmly held belief or ideal: Posey doesn’t like surprise parties as a matter of principle.
Inquiry/Enquiry Inquiry and enquiry both mean “a request for information.” Inquiry is the standard American English spelling. Enquiry is the British spelling.
Than/Then Than is used for comparisons: Posey runs faster than Chester. Then is used to indicate time or sequence: Posey took off running, and then Chester came along and finished her breakfast.
Their/There/They’re Their is the possessive form of “they”: Chester and Posey took their time. There indicates a place: It took them an hour to get there. They’re is a contraction of “they are”: Are Chester and Posey coming? They’re almost here.
To/Too To is a preposition that can indicate direction: Posey walked to school. She said hello to Chester when she saw him. To is also used in the infinitive form of verbs: Chester waited until the last minute to do his homework. Too is used as an intensifier, and also means “also”: Posey waited too long to do her homework, too.
Toward/Towards Toward is standard in American English. Towards is standard in British English.
Who’s/Whose Who’s is a contraction of “who is”: Who’s calling Chester at this hour? Whose is a possessive pronoun that means “belonging to [someone]”: Chester, whose phone hadn’t stopped ringing all morning, barely ate anything for breakfast.