The Pathless Moon
In a previous article about the Considerations Before Judgment and Radicality the Void Moon was mentioned, but not really addressed. Mostly because this topic has evolved its own sort of mythology to the point where it would have overtaken the previous article while confusing the overall message. This placement deserves its own space to fully unpack, and that is a commitment that can be made here.
The most popular definition of the Void of Course Moon is that it occurs when the Moon has perfected her last major aspect in the sign she is currently placed. The Moon is void by this definition in our first example. The Moon at 28° Virgo does not perfect an aspect to another planet before she leaves Virgo. In fact, the Moon has been void since she separated the sextile with the Sun at 22°.
The Moon changes signs very rapidly and there will be a period of time where the Moon is void (ranging from a few minutes to several hours) every two and a half days following this definition. This gives the impression that the Moon being void is a more regularly occurring astrological phenomenon that we can come to expect and is not so rare. This also makes it hard to believe that the Void of Course Moon is especially disrupting or noteworthy if it's something that happens so often.
In interpretation, the Void of Course Moon is often used to dismiss horary charts as invalid. If the Moon represents the general flow of events within the context of the question, then her not completing an aspect would mean there is no next step or "nothing comes from it" or the situation "doesn't go anywhere" so the chart as a whole and the situation that caused the question are not worth being explored. This is most often attributed to a quote from the 17th century astrologer William Lilly, but even more contemporary horary practitioners like Olivia Barclay are quick to point out that Lilly never says a chart cannot or should not be read if the Moon is void.
Alternative Definitions
It probably comes as no surprise that there are competing definitions and ideas about what the Void of Course Moon is and what it means. A more ancient definition did not use sign boundaries to qualify Void of Course, its focus was more about the motion of the Moon and her applying aspects. The Moon is Void, these authors say, when she is not currently applying to another planet within orb. There is a third definition that follows the same line of thinking, but quantifies it, saying the Moon is Void when she makes no applying aspects for the next 30°. Both definitions can often be found in the same text, such as Rhetorius.
The difference between the more ancient approaches and how we see Void of Course Moon being applied most commonly today can be seen in our example chart. Though the Moon is at the end of Virgo and will not perfect an aspect before she moves into Libra, she is applying a sextile to Mercury which will perfect in only 3°. The more popular definition will ignore this aspect, while the older definition sees it and utilizes it, refusing to see the Moon's course as void or empty when she is so close to her next planetary destination.
The older definition places emphasis on the Moon as the transmitter of influences between the planets. Her quick motion allows her to transmit the light of one planet to another and connect them together like a celestial courier service. She takes a package from one planet (in our example, the sextile with the Sun) and delivers it to the next (the sextile with Mercury) before picking up her next package at that location to take to the planet to whom she will apply next (the conjunction with Mars). This creates a series of connections between the planets that are also lunar destinations. The Moon is void, then, when she is not within orb of her next planetary contact and she doesn't know what her next destination is or it is otherwise not in reach.
Another way to think about this is to see the Moon as a trapeze artist and the other planets as her trapezes. In this chart, we see that the Moon has leapt from the Sun trapeze (because she's separating from his sextile) and is leaping towards the Mercury trapeze. Because she is within orb of Mercury we know that she will safely land there and will continue along her way. Being Void of Course is more like a trapeze artist being in the air, but also out of reach of the next trapeze in her course. We all know what happens when a trapeze artist can't connect to her next swing.
Because this definition is focused on the Moon's applications and whether or not they are in orb, it means the Moon can be void anywhere, even in the middle of a sign. Taking our example chart and setting the Moon to just after the perfection of her sextile with Mercury shows that her next aspect will be the conjunction with Mars. The Moon has a 6° orb, while Mars has 4°, so these two planets must be within 10° of one another to have an aspect that is within orb. The Moon and Mars are 12° apart, so not within orb and the Moon is void at this time.
This definition allows the Void of Course Moon to be a less consistently reliable phenomenon. It's something that can occur at any time, does not always occur at the end of a sign, and the Moon may go several days at a time without being void. This more accurately embodies the concept as one of disruption and unexpected delay than the more clockwork-like definition discussed above.
Void Moon in Interpretation
Having a Void of Course Moon in any horary chart is not immediate cause for alarm or despair. In most cases, the Void of Course Moon indicates an unexpected delay where events or developments do not immediately follow one another. Eventually, though, the Moon will aspect another planet, and that usually is our object of focus.
"Therefore, if you find the Lord of the Ascendant and the Moon void of course, joining themselves to none, proclaim the retardation of and prolongation of the matter and that the matter should be less esteemed according to what you see. And look at that planet to which the Moon is joined to first after its going forth from the sign in which it is in and judge the outcome of the matter according to that planet." -Masha'allah "On Reception"
It's really just a simple exercise of seeing what the Moon's next aspect is, interpreting that, and making a note that there will be a delay or lull in events. The idea that the Void of Course Moon indicates a deterioration of events or breakdown in the question likely stems from misunderstanding the aforementioned quote from William Lilly where he says "events go hardly on" if a horary chart features a Void of Course Moon. Today we would interpret that as meaning something like the event almost never occurs. The word "hardly" though, is actually being used as an adverb, meaning the event goes on with difficulty which is more in line with Masha'allah's use of the technique.
Much Less Impedited
All signs are created equal, but not all signs give the Moon the same amount of comfort or power. We're reminded of this in Bonatti's 146 Considerations and most famously in Lilly's Christian Astrology; the Moon is much less impedited if she is found to be void in the signs of Taurus, Cancer, Sagittarius, and Pisces. The reason why is never made explicit, but likely has to do with these four signs being the dignities of benefic planets.
Taurus is the domicile of Venus
Cancer is the exaltation of Jupiter
Sagittarius is the domicile of Jupiter
Pisces is the domicile of Jupiter and exaltation of Venus
Libra's - the other domicile of Venus - absence may seem strange at first glance, but this is likely due to this sign also being the exaltation of Saturn. Of course, we must not forget the Moon's own dignity in the signs of Taurus and Cancer.
Some have understood this aphorism as meaning that the Moon cannot be void in these signs, which is not the case. It indicates that the Moon's condition is not so bad as to slow the process down for very long. While the Moon may not be immediately ready to connect to her next destination to move the situation forward, the environment that she is in is supportive enough to keep the situation afloat in most cases.
The Breakdown
So, if the older definition of the Void of Course Moon plays into the essence of the Moon more directly and is older, why did the definition get replaced? It's hard to say. Hellenistic astrologers appear to consistently define void of course in regards to the lack of an applying aspect with no mention of sign boundaries or sign changes (Dorotheus, Antiochus, Firmicus). Sometime in the medieval Arabic tradition this gets changed as evidenced by Masha'allah, Abu Ma'shar, and others. So, something happened sometime between Firmicus (4th century) and Masha'allah (9th century) to initiate this change and what that is I cannot say at this time.
That being said, there are still sources we can point to that either give or effectively utilize the older definition. Guido Bonatti (12th century), for example, defines void of course as being when a planet separates from another planet and does not apply to a third and that being void will last until it "seeks the conjunction of another". Similarly, though William Lilly defines the Void of Course Moon in relation to sign boundaries on page 112 of his work Christian Astrology, there are examples of his work where he uses it much more in the spirit of Bonatti's definition (pg. 238, 386, 401, 467, 471).
Far from being a stricture that encourages dismissing a chart as "going nowhere", the void of course Moon is an indicator of a situation that is losing momentum and this must be woven into the overall interpretation. The Moon's next aspect will always be important for the development of the situation regardless of how much space she has to travel to get there or whether or not she has to cross a sign boundary to make it. Astrology does not have any one planetary placement that invalidates the meaning of an entire chart, but it does have the depth of symbolic meaning to help us put together an accurate narrative with a helpful message.