In reviewing the answers and comments, I get the feeling that people generally consider the two to be the roughly same thing. If this is true, why do we worry about both?
It seems to me that they are very different things:
- It exists, without me doing anything to assert it, from the moment of creation.
- Unless explicitly assigned, or surrendered, it persists regardless of licence chosen for the software.
- It grants the creator very specific legal rights and remedies (although, these may vary by jurisdiction).
- Most forms of copyright have a defined duration (usually life + 'n' years).
- In an open source project, every contributor retains copyright in their own contributions.
For the Licence
- It is a legal document
- I have to explicitly choose, or create, the license. It does not apply automatically.
- It grants users of the software specific, and limited, rights.
- Unless stated in the Licence itself, or until it is revoked, it remains enforceable in perpetuity.
Are they aspects of the same thing, or do they actually serve two different populations (producers and consumers)?