The confusion between it's and its occurs because on virtually every other word 's indicates possession, so English speakers naturally want to use it's to mean "something belonging to it." But it's is only used when it's a contraction of it is or it has. The ironclad rule - no exceptions - is that if you can replace the word with "it is" or "it has," use it's. Otherwise, it's always its.
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Instructions:
1 ~ Use a hyphen when combining two or more words to describe a word that follows. The combined words act as a single adjective: a ten-dollar bill, a three-year-old boy, a once-in-a-lifetime experience.
Don't use the hyphen if the describing words come after the word being described: A well-done steak should be well done. An over-the-top presentation was over the top.
2 ~ Use an apostrophe when a letter or group of letters is being left out to form a contraction. Remembering this simple rule will help avoid one of the most common grammar dilemmas: it's or its?
• Use the apostrophe when the word means it is.
• Leave it out for "The dog wagged its tail."
3 ~ Don't be confused about when to say "Sally and me" or "Sally and I." The simple way to check is to leave the other person out of the sentence altogether. "He spoke to Sally and I" becomes "He spoke to I." "My friends and me went to the concert." becomes "Me went to the concert." If the sentence sounds wrong without the other words, it is wrong.
4 ~ Adjectives are almost always singular. No matter how many dollars are involved, it's a twenty-dollar bill. No matter how many drugs he sells, he is a drug dealer, not a drugs dealer. The exception is when the meaning is unclear: The two countries are engaged in an arms race, not an arm race.
5 ~ Be careful about words that have masculine and feminine forms. A man is blond; a woman is blonde. The man is a fiance; his girlfriend is a fiancee. Francis is normally a man; Frances is a woman. Marion is most commonly a masculine form of the name; Marian is feminine.