It is always important to keep in mind that the copyright in a work may not be owned by the author of that work. Canadian law provides that the author of a work is generally the first owner of copyright in that work, subject to certain exceptions. For example, if a work was created by an employee in the course of their employment, then their employer may actually own copyright in the work (although the employee would still be the author).
Additionally, an author who owns copyright in a work is free to sell their copyright to someone else. They may sell their 100% of their copyright ownership, or they may divide it and only sell a portion of the copyright ownership (e.g. sell only 50% of copyright in a work) or just some of the rights included in copyright (e.g. the right to distribute in Canada). Copyright is divisible and so there may be multiple owners of copyright in a work, and each of these owners would hold different or proportionate rights to control and exploit the work.
Similarly, a work may be authored by more than one person, and so there may be multiple co-authors of a single work. In that scenario, each co-author would own a portion of the copyright in the work. The co-authors may share equal portions of the copyright, or they may have privately agreed to different shares of rights, and they can even divide different elements of a work (e.g. two writers of a song could agree that one owns the lyrics and the other owns the music, but both jointly own the song).
Copyright is “divisible” in these kinds of ways.
It is important to keep the distinction between copyright ownership and authorship in mind. It is also important to remember that physical possession is not the same thing as copyright ownership. For example, if a painter sold their painting at auction then that would not necessarily transfer copyright in the work: the purchaser may own the painting itself, while the painter may still own the copyright (and would still hold moral rights as an author).
