Apostrophes, Colons, and Dashes

• Separate contractions (it's, who's, they're) from possessives (its, whose, their) by expanding the contraction
• Form possessives for singular, plural, and irregular plural nouns (cat's, cats', children's)
• Use a pair of dashes or a pair of parentheses to set off nonessential information
• Match the punctuation on both sides of an interruption: two commas, two dashes, or two parentheses, never a mix
• Use a colon, or a single dash acting like a colon, only after an independent clause, to introduce a list or explanation

Apostrophes do two jobs. In a contraction they mark missing letters: it's = it is, who's = who is, they're = they are. In a possessive noun they mark ownership: the dog's bone (one dog), the dogs' park (several dogs), the children's toys (irregular plural, add 's). Possessive pronouns never take an apostrophe: its, whose, their, yours, hers. The quick test is to expand the contraction: if 'it is' does not fit the sentence, write 'its.' A plain plural never takes an apostrophe ('three dogs,' not 'three dog's'). A pair of dashes works like a pair of commas or parentheses to set off nonessential information, and the two marks must match: if the interruption opens with a dash it must close with a dash, not a comma. Whether information is nonessential is decided the same way as in the Commas and Semicolons lesson: it is nonessential when the noun is already identified without it ('my only sister', 'Mount Everest'), not merely when the sentence still reads as a sentence once it is removed ('The students who arrived late missed the quiz' still reads as a sentence without 'who arrived late', but the clause tells which students, so it takes no marks). Once the information is nonessential, removing everything between the paired marks must leave a complete, correctly punctuated sentence. A colon must follow an independent clause and introduces a list, an explanation, or an elaboration: 'The colors are: red, blue, green' is wrong because 'The colors are' cannot stand alone, while 'She packed three things: a map, a lamp, and a rope' is correct. Careful with the test: 'She packed three things' IS a complete sentence (subject, verb and object), so that colon is right. The wrong pattern is a colon straight after a verb or a preposition, with the object still to come: 'The colors are:', 'The job requires:', 'The kit includes:', 'such as:'. A complete clause before a colon is never the error. A colon (or a single dash) is therefore a fourth legal way to join two independent clauses, used when the second clause explains the first. A single dash can stand in for a colon under the same rule. Parentheses hold side information, and the sentence must be complete and correctly punctuated without them.

• Expand every contraction in your head. If 'it is' or 'who is' sounds wrong, the apostrophe is wrong.
• For plural possessives, write the plural first (dogs), then add the apostrophe (dogs').
• Cover everything after the colon. What is left must be a complete sentence, or the colon is wrong.
• If a dash opens an interruption, look for the second dash. A comma cannot close what a dash opened.
• Remove the text between paired marks. What remains must still be a complete sentence.