Those of us who practice horary astrology of the 17th centuries and later think we know how to identify the correct planetary significator. You give the Ascendant and possibly the Moon to the person asking the question, then locate the other house or planet representing the desired matter or person, and you are done. However, in the medieval Arab tradition of horary astrology, identifying and interpreting the querent’s significator is more nuanced.
The eighth and ninth-century astrologer Masha’allah, in his short book On Reception, describes this approach in Chapter 2. I have Ben Dykes’s translation, where the chapter starts on page 444 if you wish to follow along.
The method of finding the significator is as follows: You must determine whether the ruler of the Ascendant and the Moon is more appropriately placed, and prioritize that planet in your interpretation. We start with the ruler of the Ascendant and if it is disqualified, we then examine the Moon.
The key way to determine which is the better planet to use is the one that aspects the Ascendant, or aspects another planet that itself aspects the Ascendant, or (and this is my favorite part) it aspects another planet that aspects yet another planet that aspects the Ascendant (I trust you got that). My interpretation of this precept is that whole-sign aspects are sufficient. This would then mean that the significator cannot be in the second, sixth, eighth, or twelfth houses, since these do not form whole-sign aspects to the rising sign.
If we are looking at the Moon and she is in a sign that beholds the Ascendant, but she is void, then she is disqualified as well. Masha’allah notes that the amount of impediment (lack of contact with the Ascendant) that we run into in our analysis shows the amount of difficulty in the matter inquired about.
If neither the Moon nor ruler of the Ascendant qualify, see which one will leave its sign sooner (Masha’allah measures this by degrees, rather than by ephemeris time). The more degrees it has to go before changing signs, the more slowly the matter proceeds. The first planet the ruler of the Ascendant or Moon aspects after changing signs is the one to use as significator. Its benefic or malefic nature and dignity will tell us about the final outcome of the matter.
Example: Will the Ill Person Live or Die?
This is a very different approach from our usual, isn’t it? Masha’allah, in Chapter 3 of On Reception, gives an example horary inquiring whether an ill person will live or die. Neither the ruler of the Ascendant nor the Moon qualifies as the significator, since Mercury (lord of the Ascendant) is in the eighth sign and thus does not aspect the Ascendant. The Moon is in the ninth, in Taurus, so she does aspect the Ascendant, but she is void of course. She will soon leave her sign and square Venus in Pisces, which Masha’allah interprets as eventual healing after a long and tedious illness. Venus will eventually sextile Jupiter in Taurus, with whom she is in mutual reception, though they are yet far out of orb of each other. Masha’allah predicts that the illness would increase until Venus perfected her sextile to Jupiter, and then the disease would begin to wane.
Masha’allah then explains that if Venus had instead made an aspect to Mars, not Jupiter, the person would have died when Venus perfected the aspect to Mars. Mars in this chart rules the eighth sign, and any contact with him would lead to a much different analysis. Notice that neither the Moon nor Mercury is otherwise positioned to contact Mars – this judgment is entirely based on the planet that Venus aspects next.
We are then cautioned that a planet in the Ascendant will participate with the other significator, as will a planet in the sign (or house) of the quesited matter. If such a planet is received where it is, or has some essential dignity, it indicates the matter will go well. However, a planet in the Ascendant cannot effect or prohibit the matter on its own; that must come from the ruler of the Ascendant or the Moon.