Two expressions are homophones just in case they are distinct in derivation but identical in pronunciation. Pronouns and contractions present many homophone pairs, such as "its" and "it's," "who's" and "whose," "your" and "you're," and "there" and "their," all of which are subject to frequent confusion. What are more notable are homophones that give rise to substantive misunderstanding--not mere confusions of spelling or punctuation but a failure to understand the words that one is using. Examples: pore, v.i. You don't pour (v.t.) over a book, unless there is some liquid that you are pouring over it: to study a book attentively is to pore over it. toe the line: you might "tow a line" if you are fishing, but to fall into conformity with a policy or a standing order is to toe the line, as when soldiers stand abreast with their toes at a line. I know I had some other examples in mind but I can't think of them right now.