word choice - Since and Because

Is there any difference between since and because?

Example:

Bob gave him a candy because he was nice.

Bob gave him a candy since he was nice.

Note: If someone has a better example, please post it in the comments

Answer

I knew one English professor who was fond of saying that we should never use since instead of because. We all thought he was an idiot for saying so, but perhaps purist would be a better word than idiot. To be fair, he also said this in the context of a technical writing course, so perhaps he'd even relax his own standards in the context of casual conversation.

I found this snippet on a discussion board:

This is "purist" territory. Purists will tell you that since refers to time – specifically, the amount of time that has elapsed from a starting point. Since I started work today, I've received 57 e-mails. And they will tell you that only because (not since) shows causation. So Since I started my new job today, I'm no longer looking for employment is where you should use "because."

So, back to your two examples:

Bob gave him a candy because he was nice.

Here, the candy is a reward for the lad's nice behavior. However, this sentence:

Bob gave him a candy since he was nice.

could be construed to mean that Bob gave a candy after – not necessarily because – the boy was nice.

Practically speaking, I think the difference is trivial in your example. So long as there were no pedants in the room, you could probably get away with using the two words interchangeably. Yet there are contexts where you'd want to be more careful:

Since the industrial era began, the earth has begun warming.
Because the industrial era began, the earth has begun warming.

Those two sentences have very different meanings – in the first sentence, the temperature rise might have coincided with the dawn of the industrial age by chance. The second sentence unequivocally asserts that one caused the other.