What is the difference between a sport coat, blazer, & suit jacket?

Obviously a suit is made up of pants and a jacket that match. What I want to know is what differentiates a sport coat, a blazer, and the jacket portion of a suit? In other words, if the pants to a suit were torn, could one throw the pants away and keep the jacket as a sport coat or a blazer (assuming of course... show more Obviously a suit is made up of pants and a jacket that match. What I want to know is what differentiates a sport coat, a blazer, and the jacket portion of a suit? In other words, if the pants to a suit were torn, could one throw the pants away and keep the jacket as a sport coat or a blazer (assuming of course that the jacket is a neutral color with no pinstripes and whatnot)? Also, which is more formal a sport coat or a blazer, or are they about the same formality?

Thanks
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