I think the simplest distinction is that monogamy doesn’t entertain the possibility of a monogamous sexual/romantic partner ethically having other sexual/romantic partners at the same time.
If it’s not monogamy then it can be something else but it doesn’t have to be polyamory (swingers exist and in practice the overlap seems small). Ethical non-monogamy is a superset of most definitions of polyamory but not all because there are polyamorous people who “cheat” (break relationship agreements) and it doesn’t stop them from being considered polyamorous, just like monogamous people who cheat don’t become polyamorous (although I’d argue they become non-monogamous for the duration).
It’s probably more information to learn that someone is monogamous than to learn that they are polyamorous and learning that they are ethically non-monogamous is somewhere in the middle.
I think the simplest distinction is that monogamy doesn’t entertain the possibility of a monogamous sexual/romantic partner ethically having other sexual/romantic partners at the same time.
If it’s not monogamy then it can be something else but it doesn’t have to be polyamory (swingers exist and in practice the overlap seems small). Ethical non-monogamy is a superset of most definitions of polyamory but not all because there are polyamorous people who “cheat” (break relationship agreements) and it doesn’t stop them from being considered polyamorous, just like monogamous people who cheat don’t become polyamorous (although I’d argue they become non-monogamous for the duration).
It’s probably more information to learn that someone is monogamous than to learn that they are polyamorous and learning that they are ethically non-monogamous is somewhere in the middle.