English has dozens of words that speakers and writers often confuse because the rules governing them are odd or because the words sound alike. For example, when should you use whom instead of who, or lie instead of lay? What's the difference between principle and principal, or capital and capitol? Using the wrong word can undermine your credibility and prove embarrassing in social and professional settings. To ensure that you use proper English, you should consult the app WhichWord, which contains short and clear explanations of when to use over-confusing words in English.