When I was working at Quintus, I came up with a classification which I can simplify something like this: operating system fault Something bad happened (like a remote node going down) that was entirely out of your control. There is nothing you can do to your program to prevent this. Example: power failure. It's still your problem to clean up on your way out. resource faults your program tried to do something possibly meaningful but the system ran out of some kind of resource (cpu limit, memory limit, disc quota, &c) You might respond to this by increasing the limit and trying again. representation faults your program tried to do something meaningful but the system was unable to represent the result (integer overflow, upper case of ΓΏ in a Latin 1 system, floating point overflow on a non-IEEE system, &c) Your program isn't *wrong* but you will still have to change it. existence errors Your program tried to do something with a (typically external) resource that doesn't exist (missing file) Your program could be wrong but probably isn't. You will have to create the resource or provide a different name. permission errors Your program tried to do something to a (typically external but not always) resource that you do not have permission to do (typically writing to a read-only file) You may have named the wrong resource. If not, you may have to get the permissions for the resource changed, or ask someone else to run the program. domain errors A precondition on the input arguments of an operation was not satisfied (e.g., X/0, sqrt(-1), malformed file name, head []). Your program is definitely wrong. postcondition errors Your program invoked some operation and the precondition for the operation was satisfied, but when it completed, the postcondition was not. The operation you invoked is broken. If it's yours, you will have to fix it. If the precondition was not strong enough, it may be your program at fault. Otherwise, until you can get a fix from someone, you will have to program around it. I didn't find a simple error/exception distinction helpful, and still don't. Take the case of trying to write to "/dev/nul". This is a permission error. If the program is responsible for the name being what it is, it's a mistake in the program. If the user typed the name in, it's the user's mistake. You really can't tell without tracing each value to its origin. I dare