Just as there are two competing theories about how to define the signs (“tropical” or “sidereal”), there are also two competing theories about how to define the houses – (1) “static,” or (2) “dynamic”.¹

In the Static House system (“Whole-Sign”) every house is the same size, everywhere, all the time. In Dynamic House systems (“Placidus,” etc.), the sizes of the houses shrink and expand depending on the location and the time of year.

Dynamic Houses

Dynamic systems define the three astrological fundamentals like this:

Planets	– Celestial things that move
Signs	– The zones they move through, relative to the year (ecliptic)
Houses	– Other zones they move through, relative to the day (horizon)

Dynamic systems do not consider the zones of the day to be linked to the zones of the year. In other words, dynamic houses are not linked to the signs. Instead, the houses are directly linked to two points: the ascendant and the midheaven. A very simplified definition is that the ascendant is a reference to where the sun rises, and the midheaven is a reference to Sun’s highest point on that day.

The ascendant determines the First House, and the midheaven determines the Tenth. The distance between the two varies depending on the latitude and time of year. The smaller it is, the less space is available for houses 10, 11, and 12 (and consequently 4, 5, and 6), and the more space there is for the others. This is why Dynamic Houses shrink or expand at different times and places.

There are many different Dynamic House systems (Placidus, Porphyry, etc). They all follow this basic theory, but use different maths to do so.

Static Houses

Static systems define the fundamentals like this:

Planets	– Celestial things that move
Signs	– The zones they move through, relative to the year (ecliptic)
Houses	– The order of those zones, relative to the day (horizon)

In this system, the zones of the day (“houses”) are an effect of the zones of the year (“signs”); Houses are simply the order of the signs in reference to the ascendant.

Whatever sign currently rises over the horizon is the “first.” Whatever sign comes next is the “second,” and so on around all twelve signs. For example, if Taurus rises it is the First, which makes Gemini the Second, Cancer the Third, Leo the Fourth, Virgo the Fifth, and so on. The First House becomes identical to Taurus, because the first “house” is simply the first sign, counting from the ascendant.

Evidence for the Primacy of Static Houses

Two artifacts stand as evidence for the primacy of Static Houses:

1. The fact that we have 12 houses
2. The order we use for numbering the houses

The fact that we have twelve houses suggests that the concept of houses originates in the twelve signs (which are twelve due to the twelve complete lunar cycles during a solar year). Otherwise we should probably have as many houses as we have hours (24), or some other classical daily time unit (perhaps 8 for the classical prahara).

The order of the houses more strongly evidences the same conclusion. We do not count houses in the order that the Sun moves from the ascendant to the midheaven. Rather, we count the houses in order of the signs.

Thus it seems clear that the Sign-As-House system was the original concept, and Dynamic houses evolved later. Archaeology confirms this.

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Endnote

¹ The evolution (or “mutation”) from Static to Dynamic houses systems began when non-whole-sign static systems divorced the houses from the signs but kept their fixed sizes. Since these systems were nothing but a stage in the transition from static to dynamic I only mention them here in an endnote. Although these are technically Static Systems since their houses have a fixed size, in fact they are just the evolutionary precursors of they Dynamic Systems. So I prefer to classify them as stunted, premature Dynamic House systems. I feel that the Whole-Sign House system is really the only system categorically different from the dynamic systems.