Just as an historical interlude that some people may find interesting,
it's note worthy that modern rulerships were assigned
not because of some arduous research and investigation
- as you often hear from many modern astrologers,
but instead
by astrologers of the time, cogniscant of the tradition of rulership, basically went ahead and followed Ptolemy's logic,
by assigning the next planet out with the next sign out.
So flowing from the Sun is the rulership scheme which normally reflects back to the Moon,
but breaking this they just carried on projecting out from the sun.
So the next out from the Sun is Mercury, then Venus, then Mars, then Jupiter and then Saturn,
and then when Uranus was discovered we see astrologers explicitly invent the rulership to Aquarius
because Aquarius is the next sign out after Capricorn,
then when Neptune comes along it's assigned the next one out which is Pisces.
This is explicitly stated in the very earliest sources we have for modern rulership.
So the outer planetary rulerships came about by trying to stay true to the tradition at large
and absolutely not by channelling
or study of numerous charts.
Pluto is discovered and the pattern continues.
It is assigned to Aries and there is a conference in Germany to discuss the matter more fully.
UNANIMOUS agreement dictates that Pluto rules Aries,
and the counter idea, that some were positing at the time, that it should rule Scorpio are squashed.
Until someone beats them to print
and writes up the attributions of Pluto
and that it rules Scorpio.
The author beat them to print and published a successful book and the rest is history.
It stuck, and from that day forth Pluto magically started ruling Scorpio.
I point this out because in the context of rulership even the modern rulership scheme bows to the traditional logic as much as it can.
It does not reinvent anything, instead it recognises the superiority of the traditional schema
and tries to accommodate itself into it as much as it can.
The only exception is that
the general lack of understanding of the broader tradition by the time of Pluto amongst the basic astrologer
thanks to a deliberate watering down of astrological technique coupled with the unlucky timing of Pluto coming out when the astrological world was still struggling
to emerge from the mini-dark period it underwent
meant that one of the outers went to another sign.