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I can see that the thread is old, but because the subject is very interesting and intriguing I will try to revive it with some quotes :)

Here's what Morinus is saying about the Universal significations:
"The Sun and Saturn correspond to the father through their very nature; the Moon and Venus to the Mother, and the relationship of these stars to each other and to the other planets indicates the fortunes of the parents."
This was actually Morin's quote of Ptolomy and his Tetrabiblos, book 3 chapter 4.

Morinus then speaks about how Ptolomy and Cardanus were wrong using universal significators for the reasons:
Ptolemy, Cardanus, and others were also in error when they claimed
that in every diurnal horoscope judgment concerning the father of the
native is to be made from the celestial state of the Sun, and in a
nocturnal horoscope from the condition of Saturn, but they do not see
that this is absurd, because if the Sun were in Leo and, for example,
conjunct or trine Jupiter or Venus no child would be born anywhere on
earth during the course of that day whose father would not be fortunate
and long-lived, or on the other hand, unfortunate and short-lived if the
Sun were badly placed. And of course, as this aspect would remain in
effect for several days it is clearly foolish to suppose that during this
period every child born would have the same kind of father; this is not
only contrary to experience but would also render meaningless the
significance of the houses. And the same would hold true for Mercury
with respect to the mental qualities as long as its celestial state remained
favorable or unfavorable, and the same for Jupiter with regard to
finances, etc.
The point of Morinus is that the essential qualities of the Sun and its impact are equal for all the humans (and animals, actually all on which Sun is having impact) and that the particular determination by house would determine weather the Sun is really significator of the father or not.

Than Morinus gives an example of his own chart:
Consider my own horoscope: I was born during daytime and the
Sun, Moon, Mercury, Venus, and Saturn are in the twelfth house and
square Mars which rules the Ascendant. The Moon is therefore the
significator of the parents because it is ruler of the fourth, and of my
mother in particular since the Moon is feminine and is located in the
feminine sign Pisces; its separation from the conjunction of Saturn while
applying to no other planet indicates dislike by my parents ?
particularly by my mother ? and unfair treatment at her hands.
However, the Sun is in partile conjunction with Jupiter, and this caused
Cardinal Richelieu to be my secret enemy as this Sun is in the twelfth
along with Saturn. The Sun here is the significator of powerful enemies
and the injuries caused by them, but not of my father although 1 was
born during daylight; in fact, my father never disliked me and never
deliberately did me any harm. And so, this horoscope is an example of
how the universal significators are not able to refer to any specific
situation or event since, considered by themselves only, their meaning
and application remain too general.

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Then Morinus gives an example of the Moon being in 7th and how could be possible to refer to the Moon as being significator of the Mother as well as of the spouse?! This would be insane..
...if the Moon were ruler of the fourth house and
therefore significator of the parents and the mother in particular, it is still
located in the seventh house and by this determination through location
refers more clearly to the wife than to the mother; and so on for the other
planets and houses.
This is because Morinus constantly says in his books that the Planet is stronger by its place then by rulership of some other place.

My opinion on this matter is to always consider which planets are in 4th.
In my example, I have Moon and Mars in 4th. Can we say that they represent my mother and father? It is hard to say.
Mars rules 10th and Moon 1st.
My father is having strong influence on my career (Mars ruler of 10th is in Scorpio in 4th), so it can be that it is represented by Mars (male planet).
Moon is in Libra with Dispositor Venus (two female planets), so it can be that Moon is my Mother.
However, I'm still not sure about the whole issue of parents/houses.

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This is because Morinus constantly says in his books that the Planet is stronger by its place then by rulership of some other place.
He says this, but a closer look at what he means might be in order. The reason he gives primacy to a planet occupying a house over the planet that rules it is immediacy. In other words if the Moon is in the 7th House, ruling the 11th, and is affected by a direction, transit, etc, the effect is immediately felt in the areas of life ruled by the 7th, i.e. the partner or spouse and not the friends. However the friends might be involved in the effects of the direction, particularly if the 11th is unoccupied. Or the direction could also affect the children (11th is 5th of the 7th and opposite the radical 5th), which is more likely as there is a connection between the spouse and his or her children. But the main thrust will be the 7th and the effects on the 11th will be secondary - not necessarily weaker.

For example if the direction showed an illness to the spouse, circumstances might dictate that the children have to care for their mother and this becomes a major burden. The secondary effect is not weak; it is caused by the primary effect on the spouse.

What can be seen with this example and with the notion of general significators, is that we can obtain a greater degree of precision with Morin's method than with the general significator idea. The direction above could affect any woman in the native's life if we follow Ptolemy. If we follow Morin it can only affect the spouse directly and what the Moon rules secondarily.

In fact Cardan seems to agree with Morin, if Morin quotes him accurately*:
What must be the condition of the Moon in the horoscope of one whose wife had died in childbirth but himself lived a long life who had many healthy daughters but also maid-servants who ran away, who had a sound body but a mother who died young, and who himself showed a poor moral character?
It seems that Cardan, a promoter of Ptolemy, felt the idea of general significators could be taken too far.

*There is very little of Cardan available in English. I hope one day one of astrology's overworked translators will address this situation as I think there is much of value in his work. Cardan was a brilliant man.