I am very pleased to be posting in this forum and share my thoughts and questions regarding traditional astrology. The thing I am inquiring about is how to determine whether a planet functions as a malefic or benefic. Do these rules apply to Sun, Moon and Mercury as well?

Let's use a hypothetical chart as an example as a reference:
9th Place: Cancer Saturn
10th Place: Leo Moon (waning)
11th Place: Virgo Venus
12th Place: Libra Jupiter/Mars/Sun/Mercury

Welcome, AstroBoy!

Every planet and both of the luminaries have their good and their bad sides. It depends…

• …on how they are dignified or debilitated. A essential dignified Saturn is no more malefic, a essential debilitated Jupiter is not beneficial e.g.
• …on what houses they rule. Venus as lady of the 6th, the 8th or the 12th is not beneficial for example.
• …maybe to a lesser extent on the placement in a house. Is a dignified Jupiter able to kill if located in the 8th? Surely if he is the Anareta.
• The Sun is the giver of light but can be malefic when one comes to near.
• The Moon is moody and changeable especially when debilitated. Mercury is a trickster whom you cannot trust entirely. If they are essentially debilitated or receive hard aspects even more.

That are the cases that come to my mind now. Maybe there is more I am not aware of right now.

This question has been asked in the forums many times, just in different formats. A more recent thread:

viewtopic.php?t=12915

Here's a thread with some useful quotes and comments:
viewtopic.php?t=4832

Another one:
https://www.skyscript.co.uk/forums/viewtopic.php?t=1037

I have been looking at Indian astrology more recently, and their rules tend to be more clear, IMO, although in practice I don't see it working as well in my own natal chart.

I follow the general rule that benefics behave as benefics but when ill dignified they become debilitated in the ways of their sign and placement. This doesn't necessarily mean they are "bad," but there is something out of the norm about them, which may lead to problems in the chart (whether it is a natal chart, event chart, horary, etc- it is universal). They can still perform in positive ways, but their ability to do so is lessened and/or they may cause harm, even possibly unintentionally. Generally, the harm is not of the magnitude of an ill dignified malefic in an accidentally strong house, etc. Maybe someone can show examples counter to that but I haven't seen it myself. Malefics when good can perform well but there are usually still some downsides and disappointments somehow. Malefics when badly placed are often very destructive when given power in the chart to allow that. I have seen this too many times throughout astrology to believe otherwise. In cases where they are somehow alleviated, this will certainly help, such as being received by a strong benefic, Venus or Jupiter for Mars or Jupiter for Saturn. If they are placed in houses where they are cadent and don't behold the ascendant or the ascendant lord in any aspect, then even though they have the potential to do harm, that harm might be reigned in more.

Thank you, Tanit3333, for this more detailed description and this very interesting second link!