My aim is to suggest some reasons for different systems having been proposed in the past, and to make clear just how each system is constructed. If readers can understand how a particular system works in practice, how it relates to what is happening in the sky and the astronomy behind the house cusp calculations, they will be able to make a more reasoned choice of system for themselves.
I should point out at the start that some astrologers have suggested that different house systems are appropriate for different purposes: one system for natal work, another for mundane, another for horary, etc. I will not be discussing this further but recommend the idea as worth further investigation. In explaining how the houses are constructed, I will be using some simple diagrams, but if you are not familiar with the celestial sphere and the relationship between the ecliptic, celestial equator and horizon, before continuing with this article you may wish to read another of my articles on this website: Charts are not flat.
For those interested in more detail on house construction and some of the history I recommend the excellent book by R. Holden .
Venus enters Sagittarius
No single classification of house systems adequately covers all the many possibilities; however, following Holden's approach, we can distinguish three broad classes of house system:. Most house systems, such as Porphyry, Campanus or Placidus, produce houses of unequal size, when measured on the ecliptic. Another way to classify house systems is to distinguish quadrant and non-quadrant house systems. Quadrant systems divide the quarters 'quadrants' of the sky between the Ascendant, MC, Descendant and IC, treating these as the cusps of the First, Tenth, Seventh, and Fourth houses, respectively.
They differ in where they place the intermediate house cusps.
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These quadrant systems give Angular, Succedent and Cadent houses. A planet in an Angular house, such as the first, tenth, etc. Probably the oldest house system is the Whole Sign system not to be confused with the similar Equal House system, discussed below. This is a non-quadrant ecliptic system. James Holden, who researched early systems of house division, particularly the early Greek systems, points out  that the system used in the Hellenistic tradition was whole sign houses, or what he called the "sign-house" system.
Robert Hand in his booklet  is also of the opinion that Whole Sign houses are probably the earliest system. In this system, the first house is the whole of the sign that is rising; the second house is the next sign to rise, and so on. In figure 1 which is shown with Placidus houses , the first house is from 0 Pisces to 30 Pisces, the second house the whole of Aries and so on. If we look at Uranus, by Placidus it is in the first house, by Whole Sign, it is in the second; similarly, Jupiter is in the first by Placidus, but in the third by Whole Sign.
However, even with the Whole Sign system things are not quite that simple. Vettius Valens was a 2nd-century Hellenistic astrologer, and younger contemporary of Ptolemy.
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In his booklet, Hand  suggests that Valens used Whole Signs for determining the area of life a planet would affect, but used a quadrant system probably Porphyry to determine the strength of the planet. In most modern house systems, the same set of houses fulfils both functions: area of life and planetary strength. A problem with Whole Sign houses is that the house cusps cannot easily be used for timing events. As houses correspond to signs, a transiting planet conjunct the cusp of the first house is also sextile the cusp of the third, square the cusp of the fourth, trine the fifth, etc.
In addition, when a transiting planet moves from one house to the next it is, at the same time, changing sign. The oldest and simplest of the quadrant systems is Porphyry. The four quadrants the areas between the angles are each divided into three equal parts to get the cusps of the intermediate houses. So, in figure 1 above, the distance from the ascendant to the IC is 4PI54 to 20GE02, which is 90 degrees three signs plus 15 degrees 8 minutes, which gives degrees 8 minutes. This distance is divided by three and added to the ascendant to give the second cusp: degrees 8 Minutes divided by three gives 35 degrees 3 minutes less a third of a degree, which we will ignore.
Thus, the second cusp is at 4PI54 plus 35 degrees 3 minutes, which gives 9AR Similarly, by adding another 35 degrees 3 minutes we get 15TA00, the third house cusp. This puts Uranus in the second and Jupiter in the third. Like Whole Sign Houses, this is a non-quadrant ecliptic system. In both systems, each house is 30 degrees long; however, in Equal House the ascendant is the cusp of the first house. Therefore, in figure 1, the second house starts at 4AR54, the third at 4TA54, and so on.
One issue with this system is that, because all the cusps are at the same degree position in each sign, transits to house cusps are in fact aspects to the Ascendant: the third cusp is sextile the ascendant, the fourth cusp square the ascendant, and so on. Porphyry is a quadrant system, and so the tenth house cusp is the MC, but Whole Sign and Equal houses do not have the MC as the tenth cusp.
Depending on the latitude, the MC can fall in the 8th, 9th, 10th, or 11th house. This is often seen as a significant problem with these non-quadrant systems. This takes us back to Valens; do we use the houses as indicators of planetary strength as well as the area of life affected , or is strength determined by a planet's placement in relation to the angles? It can be argued that the ecliptic is the wrong thing to use in deciding the house of a planet.
Before deciding that there is a problem:
The sign a planet occupies determines how the principle represented by the planet will function, while the house it occupies determines in which area of life a planet will manifest its action. To use the signs or any other ecliptic based division to determine the area of manifestation seems inconsistent. It is often argued that the signs divide the Earth's orbital plane into 12 equal segments and so by analogy, the houses should divide the Earth's rotational plane the equator, or time , or the celestial sphere, into 12 equal segments.
We will consider this later. Before considering non-ecliptic based systems, I need to say something about the idea of a house cusp. The cusps have two functions. Firstly, they determine the sign ruling the house and so the house's ruling planet. Secondly, they determine the division between houses, but not necessarily the start of a house. What does that mean?
In Christian Astrology , pages 33 and , Lilly refers to a 5-degree orb of influence that precedes the cusp of a house. Suppose the second house cusp is at 15 Taurus, and a planet at 11 Taurus. Lilly, and other early authors would view the planet as being in the second house, not the first. Thus, the start of a house is about 5 degrees before the cusp. The cusps determine the house divisions, but do not mark the start of each house, which is 5 degrees earlier. This traditional view of house cusps derives from considering the cusp as the most powerful point of a house's influence.
There is a further point to consider if we allow this 5-degree orb. If we use transits or progressions to house cusps for timing of events, which point should we use?
The Tangled Web of Astrological House Systems
Is it the transit to the cusp, or the entry of the planet into the 'orb of influence' that marks the transit? This is something that would benefit from further work. In order to explain the different systems of house division and how they are constructed, I will need to use diagrams of the celestial sphere and show the various great circles, such as the equator, ecliptic, horizon, etc.
A diagram with them all shown, along with the construction of the houses, can be very confusing, so first I will show some simple diagrams, and then add extra information as needed. We start with the earth, showing the equator and the North Pole Figure 2 , this is then projected outwards onto the sky to form the celestial sphere. Note that the North Pole is at 90 degrees to the equator. In what follows, the point that at 90 degrees to any of the great circles will be called the pole of that circle. Just as the pole of the equator is at 90 degrees to all points on the equator, there is a pole of the ecliptic at 90 degrees to all points on the ecliptic, a pole of the horizon, and so on.
This is shown in Figure 3. Clearly, there are two poles, one above and one below the great circle, but it does not make any difference which we use in the construction of the houses. We will often use the pole of a great circle to 'project' points, usually onto the ecliptic.
Topocentric House System
We want the position of the house cusps on the ecliptic. If the cusps are generated by dividing the equator into 12 sections as will happen in the first system we look at below , we need to take lines from one pole to the opposite pole, crossing the great circle of the equator at right angles, and note where these lines cross the ecliptic.
Think of the lines of longitude on the earth, going from the north pole, across the equator and on to the south pole. It is easy to get confused by this. Dividing a great circle, such as the celestial equator or the ecliptic and then taking lines from the pole of the circle being divided to cross it at right angles is like dividing the earth's equator and taking lines from the geographic North or South pole to give lines of geographic longitude.
Finally, note that often we will project from the poles of the circle being divided to get the ecliptic positions, but sometimes we will use another pole. More of that when we come to it.