Parent's extramarital affairs rulership question

If the question is about, for the sake of example, my Dad, is the 7th house used for him and then the 10th house for my Mother?
Or is the 4th/10th house axis used and the 7th house disregarded completely?

The theoretical question is "Is my Dad cheating on Mom?"

This is purely theoretical of course...

Purely theoretically. If you are asking a question about your father, he gets your 4th house.

If your mother comes to you and asks a question about your father, she gets the 1st house and dad gets 7 because he is mum's spouse.

Querent pretty much always gets 1st house regardless of your relationship to them, because that person is the one asking the question. But if you are asking about someone, then they generally stay in their house. Your dad is 4, your dog is 6, your tenant is 7, your boss is 10, and so on.

Not so theoretically: If a parent comes to you asking about their spouse having an extramarital affair and cannot be dissuaded from using astrology - send them to an astrologer you are not related to!

Perfect. Thank you!

Also remember that the natural ruler's for parents are:

- Sun for father in day charts
- Saturn for father in night charts **
- Moon for mother ***

This is in case that you are doing a multi house chart, in which a lot of planets or houses are involved, and thus many houses share the same ruler.

For example in a question like:"Does my father approve my boyfriend/girlfriend?", and it happens that the same planet rules the 4th and 7th houses, and its a day chart, you can use the ruler of the 7th for your bf/gf and the Sun for your father.

This helps solve overlapping rulerships. However, you should only use them for this particular cases of multiple house questions.

As Oddity made clear in his post, the 4th/10th rule your parents. Always take the 4th and 10th as priority for them. The natural rulerships are only auxiliary signifiers, in case the main planets are already being used.

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**Some authors state that the Sun always rules the father figure, and the Saturn night counterpart is not needed. So this comes down to personal technique.

***I don't remember if Venus can also signify the mother, and if there is a day/night variable with the Moon, as in with Sun/Saturn.