I have a purple, and red hard lump that looks like a bruise on the roof of my mouth, what causes this ?

More information ...: There are many causes of a lump in the mouth, how long has it been present, is it painful, was there injury? The most common cause of a lump in the mouth is an ulcer, however there are other causes, some of which are serious and mandate Dr review. www.fauquierent.net/mouthmass.htm is a webpage with a sensible summary of causes for further information