It’s a common mistake to confuse because and since. In most cases, these words are not interchangeable. Here’s how to use them correctly and avoid confusion.
Use because to denote a specific cause-and-effect relationship.
He bought it because it was cheap.
Do not use since to mean because. Otherwise, the meaning could be unclear.
Consider the following example:
Since we tested the MacBook, we didn’t have time to review other products.
Does this mean you didn’t have time to review other products because you spent too much time testing the MacBook, or that you haven’t reviewed other products in the time since you reviewed the MacBook? They may be similar, but “since” indicates a time element.
Change to one of the following, based on the meaning:
We didn’t have time to review other products because we spent too much time testing the MacBook.
Ever since we tested the MacBook, we haven’t had time to review other products.
Occasionally, since is acceptable in a casual sense when the first event in a sequence led logically to the second but was not its direct cause. In this case, be sure to use a comma.
We ended up watching “X-Men,” since there was nothing else we wanted to see.