As you can see, spelling matters . . .
1. Who / Whom
These similar pronouns are often used to join two sentences or phrases together but they work quite differently.
“Who” refers to a subject of the sentence. This is correct: The old man, who was dressed in simple clothes, is none other than the founder of a large business corporation.
“Whom” refers to an object of a sentence. This is correct: This is the Steve, whom I met in my friend’s party. “Whom” here refers to Steve. In the second part of the sentence, Steve becomes the “object” of the sentence.
2. Its / It’s
“Its” is a possessive adjective belonging to a thing or associated with a thing. This is correct: The dog is wagging its tail.
“It’s” is a contraction of “it is”. This is correct: It’s pretty annoying to have someone talking loudly in the cinema.
3. Irregardless / regardless
There is no such word as “irregardless“. Regardless means without considering the current or the mentioned situation. This is correct: Regardless of the dangers of this operation, the firemen dashed into the building to save the victims.
4. Bought / Brought
These two words are easily misspelled because of a difference in only a letter.
“Bought” is a verb that is past tense of “buy” while “Brought” is a verb that is the past tense of “bring”.
5. Principle / Principal
“Principle” refers to a noun that is the fundamental of foundation for reasoning or belief. This is correct: I am not doing any illegal or immoral activities because this is a matter of my own principles.
“Principal” is a noun that refers to the first in order of importance. It also refers to an original sum of money for investment or loan. This is correct: With the annual interest rate of ten percent and the principal amount of the investment is a hundred thousand dollars, you are likely to receive a hundred and ten thousand dollars at the end of the investment.
6. Unless / Although / Though
These are conjunctions, which connects 2 sentences together. “Unless” works differently from “although” and “though”.
“Unless” is used to determine if a statement or event is valid or true, based on a condition that is given. If the condition is fulfilled, the statement would not be valid. This is correct: Unless you have an e-mail address, you will not be able to sign up for Facebook. This is incorrect: Unless you have an e-mail address, you will be able to sign up Facebook.
A popular mistake is the usage of “but” when using “although” and “though“. This is incorrect: Although you had done your best, but you are still unable to become one of the finalists of this competition. This is correct: Although you have done your best, you are still unable to become one of the finalists of this competition.
7. In time / On time
Both phrases work very similarly, with a slight difference in meaning. “In time” would refer to having enough time to spare to accomplish a certain task. This is correct: He was saved because they brought him to the hospital in time.
“On time” would indicate punctuality, which meets the planned time. This is correct: The meeting has to start on time.
8. At the end/ In the end
“In the end” is used to show that a long time has passed and there is a conclusion. This is correct: In the end, I received a refund for my spoilt printer.
“At the end” is to show a point where something stops. This is correct: The bulk of the movie was entertaining, but it became disappointing at the end, because it ended so suddenly.
9. At the beginning / In the beginning
This is similar to the previous one. “At the beginning” refers to a specific point of time. This is correct: You will be asked to give a simple introduction of yourself at the beginning of the lesson.
“In the beginning” refers to something that starts over a period of time. This is correct: Our ancestors faced many hardships in the beginning.