Just recently I was asked an intriguing question: what is the difference between a religious belief and a superstition? Having given it a fair amount of thought, I’ve realized that the question is quite difficult.
At the moment, my working definition of a religious belief is as follows: any belief which has reference to a supernatural entity or object.
A superstition, on the other hand, I’m leaning towards defining this way: a false belief in supernatural causation.
Defined this way, superstitions are a small subcategory of the larger category of religious beliefs. Superstitions are always false since they assume causality where none exists; e.g. walking under a ladder or breaking a mirror do not actually cause bad luck. They are religious since they assume the existence of supernatural forces.
Superstitions are always related to causation. That is, they assume that a supernatural force has caused something to happen. A religious belief, on the other hand, may or may not have anything to do with causation. For instance, a Deist who believes that God created the world and then stepped back to watch it work, believes in the existence of a supernatural being (God), but does not believe that this God intervenes in the world. Thus, apart from the initial creative act, the deistic belief in God does not entail any belief in causation, but since it posits a supernatural entity (God), it is still religious.
Religious beliefs can be true or false, of course, but superstitions are always false. I suppose to be proper we should talk about true religious beliefs and false religious beliefs and understand that superstitions are actually a subcategory of false religious beliefs. Thus the belief that God is not a Trinity is a false religious belief (because He is) but not a superstition. The belief that an angel gets her wings every time a bell rings is a superstition because it is a false religious belief related to causation.
As I see it, we cannot always tell if a belief is strictly superstitious or merely religious in the more general sense. Some things will fit easily into either category but others we will not be able to pigeonhole so neatly, given our finite knowledge.