\u201cAllusion\u201d and \u201cillusion\u201d are both fairly rare words. They also sound similar, making it is easy to confuse them if you\u2019ve never seen them written down. But these terms have very different meanings, so make sure your work is error free by checking out our guide to how they should be used.\nAllusion (Indirect Reference)\nAn \u201callusion\u201d is an indirect reference to something. For example, the title of David Foster Wallace\u2019s novel Infinite Jest is taken from a line in Hamlet. This is an \u201callusion\u201d to Shakespeare \u2013 rather than a direct reference \u2013 because Wallace does not mention Shakespeare or Hamlet in the novel.\n\nAnd while \u201callusion\u201d is a noun, the verb form of this word is \u201callude\u201d:\nThe title of the novel alludes to Act 5, Scene 1 of Hamlet.\nAgain, the key here is the idea of referencing something indirectly.\nIllusion (Mistaken Perception or Belief)\nThe word \u201cillusion\u201d usually refers to a mistaken sense perception, such as a mirage. As such, we could say something like:\nHe saw the hazy outline of an oasis, but he knew it was an illusion.\nThis idea of seeing or sensing something that isn\u2019t really there is also why we say magic tricks are \u201cillusions,\u201d as well as why we call trick images optical illusions. But we can also use \u201cillusion\u201d to describe a false belief:\nI was laboring under an illusion to think I could run a marathon.\nHere, \u201claboring under an illusion\u201d means acting on a mistaken belief.\nSummary: Allusion or Illusion\nThese words have many letters in common, but they differ in meaning:\n\n \tAn allusion is an indirect reference to something.\n \tAn illusion is a mistaken sense perception or belief.\n\nOne trick to remembering this difference is the phrase \u201cOptical illusions will make you ill.\u201d This can remind you that \u201cillusion\u201d starts will an \u201ci,\u201d like the word \u201cill.\u201d But if you\u2019d like to make extra sure your writing is always error free, you can always ask a proofreader.