Persons who share bodies still have distinct legal and social existences, so if one commits a crime, the other is entitled to walk free while awake as long as they come back before sleeping—but how do they prove it?
Is this a realistic cultural adaptation? In most human societies if you are stuck working or living with someone your social existence is somewhat shared. A person from your clan doing something bad is a also bad for your own reputation. If someone from your family committed a crime some legal traditions would hold you responsible. It seems much more plausible that society would consider the two people living in the same body to be legally treated at least like a married couple or brothers where in some past ones.
Given your constraints and assuming no cheap and easy test of distinguishing them, of all historical examples I can think of, only modern Western culture with its hyper-individual liberalism would bother with the impracticality of treating the two people like two fully distinct individuals. And even then they would have to give a family-like if not legal guardian-like relationship for the issue of making medical decisions. Not sharing your place of residence and ownership over it would be impractical, though perhaps there would be a strong norm of not going into the other guys part of the house.
Also as a minor note the culture would probably develop a norm of some sort of marker (perhaps clothes, jewellery) or face paint to show which of the two persons in currently in control. The distinction would be more or less universal not simply individualized so even strangers could tell this was two different persons. Think more “Ah I see your patron god is the first twin Jahu. Your cohabitor was here yesterday.” instead of “Aha James always wears his leather jacket you must be Harry!”. Using the wrong marker would probably at least as taboo as cross-dressing was in some past cultures.
I’m not trying to get too much into the cultural details here—certainly cultures vary in the setting. Some of them do treat cohabiting like it’s on par with marriage, and even arrange it through families (which makes sense: if we want to share grandchildren, we arrange for our kids to get married if they’re the opposite sex, but if they’re the same sex nonfantasy humans are out of grandchildren-sharing luck. In comes cohabitation!) But importantly, cohabitors cannot talk to each other. There is no way for them to socially pressure each other outside of self-destructive attacks or sternly written letters. You could hold someone responsible for what their cohabitor did, but this would only deter people who were compassionate enough to care about the fate of someone they cannot ever interact with—and, if they picked each other instead of being arranged, chose on the basis of not particularly desiring to ever interact with them again. (You don’t pick your friends as cohabitors: you pick people whose company you don’t care for with comparable danger tolerances and cosmetic features you want to include when you have your bodies conglomerated.)
Also, they don’t sleep, so “place of residence” dissolves for most people. They have typical hangouts, storage lockers, clubhouses and favorite restaurants and rental kitchens—but why bother maintaining an entire house? You don’t need a secure place in which to sleep; your cohabitor will look after your body while you’re unconscious. Medical decisions are also made a lot simpler by the magic system, although they don’t completely go away and there’s probably some plot to be had there.
Most people would probably adopt cosmetic markers, but how required these would be would certainly vary; I think your expectation here would be a reasonable way for one society to operate but too sweeping for all. This isn’t how we treat identical twins, who, while uncommon, are still a known feature of the real world. I look a lot like my sister to the point where one time I walked into her school and six of her friends mistook me for her; we were not then obliged to choose distinct ritual scarves and wear them at all times.
How much of a status symbol would a home be? Only the poorest don’t have a home? A home is a middle-class sort of thing? Only the rich? Only the very rich?
Is this a realistic cultural adaptation? In most human societies if you are stuck working or living with someone your social existence is somewhat shared. A person from your clan doing something bad is a also bad for your own reputation. If someone from your family committed a crime some legal traditions would hold you responsible. It seems much more plausible that society would consider the two people living in the same body to be legally treated at least like a married couple or brothers where in some past ones.
Given your constraints and assuming no cheap and easy test of distinguishing them, of all historical examples I can think of, only modern Western culture with its hyper-individual liberalism would bother with the impracticality of treating the two people like two fully distinct individuals. And even then they would have to give a family-like if not legal guardian-like relationship for the issue of making medical decisions. Not sharing your place of residence and ownership over it would be impractical, though perhaps there would be a strong norm of not going into the other guys part of the house.
Also as a minor note the culture would probably develop a norm of some sort of marker (perhaps clothes, jewellery) or face paint to show which of the two persons in currently in control. The distinction would be more or less universal not simply individualized so even strangers could tell this was two different persons. Think more “Ah I see your patron god is the first twin Jahu. Your cohabitor was here yesterday.” instead of “Aha James always wears his leather jacket you must be Harry!”. Using the wrong marker would probably at least as taboo as cross-dressing was in some past cultures.
I’m not trying to get too much into the cultural details here—certainly cultures vary in the setting. Some of them do treat cohabiting like it’s on par with marriage, and even arrange it through families (which makes sense: if we want to share grandchildren, we arrange for our kids to get married if they’re the opposite sex, but if they’re the same sex nonfantasy humans are out of grandchildren-sharing luck. In comes cohabitation!) But importantly, cohabitors cannot talk to each other. There is no way for them to socially pressure each other outside of self-destructive attacks or sternly written letters. You could hold someone responsible for what their cohabitor did, but this would only deter people who were compassionate enough to care about the fate of someone they cannot ever interact with—and, if they picked each other instead of being arranged, chose on the basis of not particularly desiring to ever interact with them again. (You don’t pick your friends as cohabitors: you pick people whose company you don’t care for with comparable danger tolerances and cosmetic features you want to include when you have your bodies conglomerated.)
Also, they don’t sleep, so “place of residence” dissolves for most people. They have typical hangouts, storage lockers, clubhouses and favorite restaurants and rental kitchens—but why bother maintaining an entire house? You don’t need a secure place in which to sleep; your cohabitor will look after your body while you’re unconscious. Medical decisions are also made a lot simpler by the magic system, although they don’t completely go away and there’s probably some plot to be had there.
Most people would probably adopt cosmetic markers, but how required these would be would certainly vary; I think your expectation here would be a reasonable way for one society to operate but too sweeping for all. This isn’t how we treat identical twins, who, while uncommon, are still a known feature of the real world. I look a lot like my sister to the point where one time I walked into her school and six of her friends mistook me for her; we were not then obliged to choose distinct ritual scarves and wear them at all times.
Cohabitors could also pressure each other with rewards, and with threatening to withhold rewards.
I’m not sure about the lack of residences. A storage locker isn’t the same thing as having your stuff conveniently arranged for use.
Well, houses are at least a great deal more optional. I’m imagining them as something of a status symbol.
How much of a status symbol would a home be? Only the poorest don’t have a home? A home is a middle-class sort of thing? Only the rich? Only the very rich?
Again, would vary from culture to culture within the setting.
IIRC, in some cultures (e.g. mid-20th-century Italy) they did the opposite, i.e. they dressed their twin children identically.