[PaulDavisThe1st]

both clauses above are false.

There are plenty of commons that come with borders, the most trivial of which would be a patch of land used for grazing livestock.

Garrett Hardin himself has acknowledged that he made a mistake with the concept of "the tragedy of the commons". There is no such thing. Commons have all historically been carefully managed by a complex interlocking web of understandings, traditions, rules. The so-called tragedies correspond to (essentially in every case) powerful interests ignoring or overthrowing the management structures governing a commons to pursue their own self-interest.

[Sharlin]

What I meant was, obviously, that commons are not internally divided, otherwise they would not be commons.

Yes, commons have historically been managed, or should I say coordinated [1], more or less explicitly, exactly so as to avoid the tragedy of unmanaged commons. The environmental awakening in the 20th century was a response to several tragedies of commons hitherto unmanaged, and these tragedies were partially mitigated by nation state level coordination. A couple of decades later humanity succeeded in solving the first truly global tragedy of commons in the history, the depletion of the ozone layer. But that was a relatively easy problem to solve compared to carbon emissions.

[1] https://slatestarcodex.com/2014/07/30/meditations-on-moloch/