This section is from the book "Understanding Astrology", by Ezequiel Gonzalez. See also Joanna Martine Woolfolk - The Only Astrology Book You'll Ever Need.
The traditional meanings and symbols of Astrology are not the result of scientific procedures or statistical conclusions. Astrological symbolism emerged out of over 4,000 years of astrological practice.
The usefulness of these symbols have been verify by thousands upon thousands of astrologers who have used and refined them over and over again. In their daily practice the ancient astrologers like their modern counterpart had very little use for statistical analysis. When you are facing a client who is asking you specific questions and demanding specific answer the generalizations brought about by statistical analyses are of little use. You must give the client specific answers that satisfy him. Thus the astrologer willingly or not is forced to rely on intuition, and intuition goes far beyond what a mere statistical analysis can do.
At it more superficial level intuition consist on the immediate comprehensive analysis of all the information available in order to reach a given conclusion. This analysis takes place at the level of the subconscious; to the conscious mind it appears as if the answer just popped out all by itself. In reality, however, the equivalent of many hours of detailed analysis and evaluation was done subconsciously. This is something that does not happens all the time, but when it does its answers are usually correct.
At an intermediate level the subconscious mind gets in touch with the collective subconscious mind of mankind (using Carl Jung's terminology) and gets its answers from there.
At yet a deeper level, the subconscious mind expands itself beyond the limitations of the physical body, goes out into the outer reality, perceives what is actually there, analyzes it and reach the corresponding conclusions.
Over the last 4,000 years astrologers have been forced by the very nature of their professional practice to rely on all these levels of psychic intuition. Furthermore, the results of their efforts have been tested in actual practice. Those astrologers whose advice was found lacking in depth and understanding were eventually discarded and only those whose advice was found worthwhile were successful. Likewise, the astrological community was forced to test the various refinements and interpretations proposed by different astrologers. As a result both the definitions and the symbolism of Astrology have been refined continuously over the last 4,000 years.
This highly refined body of astrological symbols had to be related to the cosmos for, after all, was the cosmic influence the one being studied. Of all the astronomical variables the ones most clearly visible were the ecliptic (the apparent path the sun traces against the background of the fixed stars as it completes its yearly cycle), and the four angles (sunrise, zenith, sunset and nadir). Thus as mankind sough to explain the cosmic influence in terms of their understanding of the cosmos, they naturally used and develop a set of symbols based on the four angles and the ecliptic path. The former became the System of Houses and the later the Zodiacal signs.
In order to present these symbols in a coherent manner they developed the Natal Chart or Horoscope. This is a graphical representation of the position of the Sun, Moon and Planets at the precise moment of birth, as percieve at the precise location of birth. In order to identify the relative positions of the planets and their symbolic states this map was divided simultaneously in twelve signs and twelve houses. The Signs divisions is based upon the yearly Earth-Sun cycle while the Houses divisions are based upon the daily cycle brought about by the rotation of the Earth upon its own axis.
Thus they represent diferent things, but for sake of convenience they were combined into a single graphical representation. Furthermore, since they served to clasify the same set of cosmoc data, it was felt that a given relation or correspondence existed between signs and houses.
This correspondence was expanded to include signs, houses and planets. The planets, as the actual visible and "real" objects in the sky were considered the active forces influencing mankind. The signs were then seen as the cosmic regions that would modify or mold de influence of the planets. Finally, the houses were senn as representing everyday affairs, the worldly concerns.
To these correspondences they added the concept of aspects, or angular distances between planets. The ecliptic was perceive as a sphere and those distances between planets that divided the spere a whole number of times were considered as connecting the planets among themselves. Theoretically, the number of such angles would be infinite, but in practice (remember that back then there were no computers to do the math; neither they had printed Ephemeris or table of houses) they only used the conjunction, (when two planets ocupy the same ecliptic position), the oppossition (when they are at opposite ends of the ecliptic), the trine (when the distance between them is 1/3 of the ecliptic) and the square (when the distance is 1/4 of the ecliptic).
Those aspects that divided the ecliptic an even number of times were considered negative or malefic, while those that divided it an odd number of times we re considered positive or beneficial.
The ecliptic was considered a circle divided in 360 degrees. Since the ecliptic was a representation of the Yearly Earth-Sun relationship, they needed to establish a given point as the starting point or 0 degrees mark. Perhaps borrowing from the Old Testament Command recorded in Exodus 12:1-2, or perhaps because of its correspondence with the Spring Season in the northern hemisphere, the fact is that the astrologers of yonder choose the Spring Equinox as the beginning of the Ecliptic. Starting at this point they divided the year in twelve sectors, known as Aries, Taurus, Geminis, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarious, Capricorn, Aquarius, and Pisces. The day was likewise divided in twelve sectors starting at sunrise.
 
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