In the Sacred Geometry of ancient Egypt and Greece, the Odd numbers were considered Masculine, and the even Numbers were considered Feminine, from this idea, the concept of Polarity was developed.
The Polarities of the Zodiac Signs were primarily based on Pythagorean Metaphysics. The twelve signs were numbered in order, with Aries being the first, and Pisces being the twelfth.
It must be understood that this does not have anything to do with sexual orientation or physical attributes. It's hard to conceive that the ancients would have let a contradiction like the idea that a Bull is used as a representative of a feminine sign slip through their rigorous philosophy. What they were more likely to be driving at was something like the polarities of Chinese metaphysics, the Yang and the Yin. Modern people can easily use electricity as an analogy, in which the current flows from one pole to the other; that's how we are able to use electricity, because without its flow, it simply is not the same thing.
The Fire Signs, Aries, Leo and Sagittarius, are placed at positions 1, 5 and 9 in the scheme of the Zodiac, and are therefore odd-numbered Masculine or Positive Signs. The Signs of Positive, or Masculine Polarity can be seen as "aggressive" rather than "man-like", because this is reflective of their elemental nature. Fire is certainly aggressive and opportunistic, and we use it to make our lives more comfortable by having it destroy wood or other forms of fuel for us. But it's not always easy to control, as in the case of huge forest fires or nuclear meltdowns. The warmth of the Fire Element penetrates everything it is near and is stimulating in its action, more qualities that were considered masculine by ancient philosophers.
The Air Signs, Gemini, Libra and Aquarius are the 3rd, 7th and 11th signs of the Zodiac, the other odd numbers. They are also considered Masculine Signs, and therefore aggressive, penetrating and stimulating. We can look at video footage of hurricanes, or think about how the cold winds of winter penetrate normally warm clothing to get a sense of how the ancients looked to nature as the source of their wisdom. We have only a little control over the wind, and usually, that control is based on capturing it when it goes into motion. Examples would be sailboats, which, in ancient times, were dependent on a kind wind. It's no wonder that they thought the winds brought luck, prosperity and fortune.
The Earth Signs, Taurus, Virgo and Capricorn, are the 2nd, 6th and 10th signs of the Zodiac respectively. These are even numbers and therefore they are considered to be of Feminine or Negative polarity. If we look at the signs of Negative polarity and consider them as "yielding" instead of "woman-like" a clearer picture emerges. The Earth certainly gives way to our human ambitions; we can use Earth to build shelter to protect us, and when left alone it provides the medium necessary for the growth or protection of all living things. Protectiveness and supportiveness are two of the other attributes of the Feminine polarity.
The Water Signs are Cancer, Scorpio and Pisces, the 4th, 8th and 12th signs of the Zodiac, and therefore even-numbered Signs of the Feminine Polarity. Our whole way of life is based on our need for water, the most vital necessity for living things. Although we use wells and tanks to control it, we also respect it, because it can consume all things, eventually. Water can be treacherous, but it's dangers are due to either our inability to control it, or because it has been stimulated by the wind. There are many secrets in the depth of the oceans that we don't understand, and pure water is becoming far more scarce than gold.
Everyone has both masculine and feminine components in their psyche, just as every horoscope includes all the signs and planets. The masculine or feminine Polarity of the signs gives a sort of guideline as to how you relate to the masculine and feminine qualities within yourself, and how this inner relationship is reflected in your relationships with others. Much of this has to do with the dominance of cultural paradigms, as well as the psychological make-up of the individual. Polarity and Elemental balance are more of an intermediate study in Relational Astrology, but it's likely that even a brief look at the subject will provide useful information.
For more information, visit our page on Polarity in Relationships to get a better understanding of how Polarity effects compatibility and relationships in particular.