The justification for all the blood-purity laws and customs, Amelia had learnt as a child, was that generations of magical ancestry had made Purebloods more magically powerful than half-bloods, and half-bloods more magically powerful than Muggle-borns. Purebloods also—so it was claimed—knew more spells than Muggle-borns did, by the time they were seventeen, because Pureblood children began learning about magic as soon as they could talk.