While I understand this is generally assumed to be true I don’t think it’s supported by good astrological logic.
The person you are borrowing money from is represented by the seventh house and their money is the eighth house.
If they give money you their money it’s now in your possession and your possessions are represented by the second house. Maybe it’s loaned to you with all sorts of conditions attached but it’s still in your possession until you pay it back. It’s in ‘your pocket’.
We can’t call money you have borrowed shared money because unless you pay it back the lender can’t access it, and therefore it’s not really shared. Even if there are legal agreements that you should pay it back, while the money is in your possession it is represented by the 2nd house, because the second house represents assets in your possession.
House meanings not constrained by law or ethics
The houses do not by themselves carry meaning relating to legal or ethical constraints. They relate only to simple realities, and the second house is specifically related to one’s movable possessions and assets. It doesn’t matter whether the money in your spouse’s bank account or pocket is earned, stolen, borrowed or whatever. If it’s currently in their possession then it’s ruled by the eighth house. If someone borrows money from you, then this money is in their possession (the eighth house) until they pay it back to you, and is no longer represented by your second house.
The eighth house is often referred to as shared resources due to the loose definition of the seventh house as “other people” and therefore the eighth house as “other people’s money”. However when we are looking at a chart, whether it be natal or horary, the question usually concerns a specific person, not an amorphous group of unidentified people.
The second house shows your money and your bank account. Even if this account is shared with your partner it’s still one of your movable assets and is represented by your second house. However if your partner empties this account then your money is gone and it’s now in their possession and is represented by the eighth house in your horoscope and by the second house in their horoscope.
Me and you
However if we do accept the idea that the eighth house represents money shared between you and me, then we have to accept that the seventh house represents us together; you and me. However I can find no astrological authorities, ancient or modern, who support this idea. In one’s natal chart the first house represents me and the seventh represents the other; usually the spouse or partner, the open enemy or person we are in contention or doing a deal with. But the seventh is never “us”. The foundation principle that can be traced all the way back to the beginning of horoscopic astrology is that the first house represents me and the seventh house represents you.
If we defy this basic logic then and say the eighth house represents us together, then what does the first house represent? It cannot represent me because I am now part of the eighth house. And what about you? Are you now only part of a joint entity and not an individual person? It really doesn’t make sense. If something doesn’t make sense then it’s nonsense.
In horary astrology if the question concerned us together, for example Will we travel to Spain next year? then the first house would represent us together. Horary astrology is very contextual. Following the same logic, if the horary question is: Will our money grow this year? then we would look at the ruler of the second house. But the seventh house is not used to represent us nor is the eighth house used to represent our money.
The same logic is employed when a question is asked about a group that the querent identifies with, such as a football team. For example, Does my team have enough funds to build the new stadium? My team is represented by the first house, and its funds are represented by the second house.
I am proposing that the popular logic for describing the eighth house as borrowed money or shared money, or ‘our money’, is flawed, and needs a rethink. It simply does not make sense that the eighth house can be shared money unless the seventh house also represents us together as this would undermine the fundamental meaning of the houses, namely that the first house represents the chart-owner (the native) and the seventh house represents their partner or opponent. The seventh house can never include the chart-owner as that would invalidate the meaning of the first house.
Astrology is beautiful in its simplicity. The second house always represents the money in our bank account and our movable resources and possessions, whether or nor someone else has access to these things. Its meaning is related to movable resources that support us and is not invalidated by the fact that someone else can access these resources or whether there are legal or other claims on these resources.