Mixing up "must have" and "must of" is one of the most common grammatical errors in English writing. But why do so many people make this mistake? And how can you make sure your writing is always error free?\r\nIn this post, we explain everything you need to know.\r\nThe Error: Using "Must Of"\r\n"Must have" is a common phrase in various situations. For example:\r\nI must have left my shoes outside. \u2713\r\nYou must have been tired after that late night. \u2713\r\nI must have some cake later. \u2713\r\nThe first two examples are the most important here, as these are the ones people are most likely to get wrong. This is because people often pronounce "must have" as "must\u2019ve" when using "have" as an auxiliary or helper verb, and "must\u2019ve" sounds a lot like "must of." For instance:\r\nI must\u2019ve left my shoes outside. \u2713\r\nI must of left my shoes outside. \u2717\r\nYou must\u2019ve been tired after that late night. \u2713\r\nYou must of been tired after that late night. \u2717\r\n"Must\u2019ve" is simply a contraction of "must have." Combining the words like this is fine in less formal writing or speech and makes grammatical sense.\r\n"Must of," on the other hand, is almost always a mistake. As a result, you should avoid this combination of words in most cases.\r\nSummary: Must Have or Must Of?\r\nIf you struggle with this phrase, try to remember the following:\r\n\r\n\t"Must have" is a common phrase used in many contexts.\r\n\t"Must of" is almost always a mistake.\r\n\r\nAs such, if you\u2019re tempted to use "must of" in your writing, you should make sure you don't mean "must have" instead.\r\nAnd if you would like any more help with the grammar or spelling in a document, don\u2019t forget that we have expert proofreaders available 24\/7.