To make matters even more confusing, both words happen to be pronounced exactly the same way. Just as there are instances where you may mistake allusion and illusion, you might also mistake canon for cannon (or vice versa). So, what’s the difference?
Canon can have several meanings, most of which are similar in scope. It could refer to a rule or a body of rules that are generally understood as fundamental to a field. You could say the Romantic Age holds the works of Wordsworth and Coleridge among its canon of poetry, for instance.
When it comes to a fictional universe, as would be the case in comic books, the “canon” is the body of material that is considered to be the “official” part of the story. For the X-Men, as an example, the canonical tale would say the original members are Professor X, Cyclops, Iceman, Angel, Beast, and Jean Grey. Non-canon, as is the case in the upcoming First Class movie, would include characters like Emma Frost and Havok.
Canon also happens to be the brand name of digital cameras and other digital imaging equipment like camcorders, scanners, and printers.
Cannon on the other hand, refers to a large artillery gun. The heavy gun can be on wheels, attached to a tank, or used in tandem with any number of military vehicles. A cannon is the weapon that makes use of gunpowder (or some other explosive-based propellant) to shoot cannon balls, bombs, and so forth.
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