> Do your tweets belong to Twitter (e.g. can they delete/modify your content once it's on their servers)?
You are conflating physical control of something with control of copyright.
The right to delete or modify content isn't the same as copyright. If you write a Wikipedia article, you own the copyright. You license the copyright with a non-exclusive, royalty-free license (Creative Commons) and you put it in a form that practically invites deletion and modification. But that deletion and modification doesn't change your ownership of the original copyright.
On a much simpler level, if I buy a current pop music album on CD, I have the right to "delete/modify" the content. I could put the CD through a wood chipper or drop it from a very high building or any number of other things. None of these would change the copyright status of the album.
> If you post a work on a public site, without explicit copyright, are you granted an implicit copyright?
No. You grant whatever copyright the terms and conditions say you grant. If there is no explicit grant, there is no implicit grant either.
You are conflating physical control of something with control of copyright.
The right to delete or modify content isn't the same as copyright. If you write a Wikipedia article, you own the copyright. You license the copyright with a non-exclusive, royalty-free license (Creative Commons) and you put it in a form that practically invites deletion and modification. But that deletion and modification doesn't change your ownership of the original copyright.
On a much simpler level, if I buy a current pop music album on CD, I have the right to "delete/modify" the content. I could put the CD through a wood chipper or drop it from a very high building or any number of other things. None of these would change the copyright status of the album.
> If you post a work on a public site, without explicit copyright, are you granted an implicit copyright?
No. You grant whatever copyright the terms and conditions say you grant. If there is no explicit grant, there is no implicit grant either.