There is a theory which states that in the planetary relationship known as a T-Square -- in which two planets or points are in opposition (180 degrees apart), with another body at their 90-degree midpoint ("squaring" them) -- the squaring planet and its opposite point (whether occupied by a planet or not) represent areas requiring personal focus and effort in order to maximize their usefulness.
For example, if your Ascendant were 17 degrees Pisces and your Descendant were 17 Virgo (the Descendant always being opposite the Ascendant), and if you had a planet at 17 Sagittarius, the third planet would be squaring both the Ascendant and the Descendent, and would thus be the focal point of a T-square. The focal planet's opposite degree (17 Gemini) would also represent a "sore spot" in the unconscious that needs at least as much attention as the planet at 17 Sagittarius, because Gemini and Sagittarius form an interrelated axis or pairing of influences.
T-Squares (as well as almost any aspect and aspect combination) can exist in relation to both planets and points ("points" would include the Ascendant and Descendant, and other abstract astrological critters like, such as the Part of the Fortune).
If the opposite point of the focal planet of a T-square were to be occupied -- as, say, would be the case if a planet were found at 17 Gemini in the example above -- we would have a Grand Square and not a T-square. This would underscore the importance of striving to work harmoniously with the principles represented by all of the planets and points involved in the aspect picture.
Trines (120 degree aspects) and sextiles (60 degrees) act as helpful outlets for energies involved in a T-Square or Grand Square (the Grand Square, especially, tends to operate in the manner of a closed circuit). If a planet involved in a T-Square or Grand Square also trines or sextiles another planet, then that combination can be a big help in approaching the energies of the square configuration.
The T-Square is thought to be less tense than the Grand Square, but in both cases the modality -- cardinal, fixed or mutable -- in which the squares fall is highlighted.
The late astrologer Dane Rudhyar is the man to whom we owe most of our contemporary understanding of this issue of T-Squares, Grand Squares and their outlets.
