Saying Origin

[bekahj77]

Does anyone know where the saying "I swear on my mother's grave" came from?

[babthrower]

Well, it's pretty obvious that one swears 'on' something he respects or reveres e.g. the bible. So one would respect one's mother's grave. The implication is that what one says is the truth. Of course, if the mother in question is still living, it's a way to tell a lie while seeming to make a serious oath that it is true.