Astrology compatibility (also called Synastry) is a complex field. Our home page has a less detailed explanation of compatible astrology signs if you just want a broad overview. The following article goes into things in a little more depth, however it's still a simplification. Many exceptions exist to almost every rule, and more complex tricks and factors are used by individual astrologers. With astrology the devil is always in the details, and sadly the details are always the first thing to be removed when sharing information! This will however give a good flavor of some of the principles involved.
Because the zodiac is split into 12 signs, units of 30 degree measurement are commonly discussed (12 times 30 being 360 degrees, which is a full circle). These have some odd names, but are quite easy to understand:
30 degrees apart = semi-sextile (neighboring signs in the zodiac wheel)
60 degrees apart = sextile (2 signs apart in the zodiac wheel)
90 degrees apart = square (3 signs apart in the zodiac wheel)
120 degrees apart = trine (4 signs apart in the zodiac wheel)
150 degrees apart = inconjunct (5 signs apart in the zodiac wheel)
180 degrees apart = opposite (6 signs apart in the zodiac wheel)
Astrology uses a duodecimal (base 12) number system. Just like music theory (which also uses a base 12 system) there are intervals which are more harmonious than others. The 12 zodiac signs provide a convenient unit of measurement (similar to hours on a clock). The zodiac signs themselves could be renamed or removed; astrology works just fine without them (it's just harder to discuss when it's more conceptual).
Same signs - tend to be very similar. For relationships this is typically harmonious but sometimes dull.
Semi-sextile - Hard to understand or relate to each other sometimes.
Sextile - Harmonious. You appreciate one another's style and it's easy to work as a team.
Square - Bad. It's hard to understand each other's style, and arguments are likely.
Trine - Excellent. Your styles are similar enough to understand, and different enough to be exciting.
Inconjunct - Paradox. If an attraction exists, it's typically very powerful, but it's hard to find the reason for it.
Opposite - Opposites attract. An all or nothing placement (common in soulmates). You find each other fascinating and (if not soulmates) frustrating.
Venus - affection, attraction and romantic love
Mars - sex and passion
The Moon - emotional understanding, support and harmony
The Sun - honor, respect and appreciation
All the other planets also play a part.
The number 12 is the smallest number with five factors (1, 2, 3, 4, 6). As a result of this high factorability duodecimal (base 12) representations fit more easily than decimal (base 10) ones into many common patterns. Within the base 12 system are other systems such as base 4 (qualities - cardinal, mutable, fixed), base 3 (elements - fire, water, air, earth), base 2 (polarity - positive, negative). These labels make the subject easier to remember.
People of Water signs tend to be emotional, sensitive and more spiritual than average. Often they relate better to people of other Water signs. Their feelings run deep and they can be easily hurt (though they often hide this vulnerability). They tend to be very loving and romantic and take relationships very seriously. The water signs: Cancer, Scorpio, Pisces
Water signs tend to get along harmoniusly with other water signs, they do well with air signs. Water and fire is typically bad. Water and earth is somewhere in the middle.
People of Fire signs tend to be outgoing, energetic, passionate, adventurous, direct and ambitious. They typically don't mind taking the occasional risk to get ahead. They usually enjoy living for the moment and prefer romance to be fun and exciting. Compared to other elements they tend to be slightly more aggressive and confrontational. The fire signs: Aries, Leo, Sagittarius
Fire signs tend to get along harmoniusly with other fire signs, they do well with air signs. Fire and water is typically bad. Fire and earth is somewhere in the middle.
People of Earth signs tend to be practical, loyal, responsible, down to earth and cautious. They tend to prefer to plan things down to the last detail and to avoid unnecessary risks (they don't get a thrill from risk taking like some other signs do). They typically prefer long term relationships over one night stands, and are often more concerned with practicalities than being swept off their feet, and tend to value stability and loyalty from a partner. The earth signs: Taurus, Virgo, Capricorn
Earth signs tend to get along harmoniusly with other earth signs, they do well with water signs. Fire and earth is typically bad. Earth and air is somewhere in the middle.
People of Air signs tend to be friendly, outgoing, and easy going. They love to socialize, talk, party, dream, meet new people and try new things. Typically they hate being bored or stuck in dull routines. When single they tend to be very good at flirting. When in a relationship they typically like a high level of independence and generally dislike to feel restricted. The air signs: Gemini, Libra, Aquarius
Air signs tend to get along harmoniusly with other air signs, water signs and fire signs (the most adaptable signs in this area). They don't typically do so well with earth signs.
When we look at a persons entire natal chart they typically place a high value on the elements they lack. For example someone with very heavy fire and earth influences typicaly finds someone with very heavy water and air influences highly intriguing. Soulmates are always opposites in this area.
People of positive signs tend to be extrovert, confident and optimistic (when compared to people of negative signs). They typically relate better to people of other positive signs (though their soulmates are typically of negative signs).
The positive signs: Aries, Gemini, Leo, Libra, Sagittarius, Aquarius
Positive signs tend to relate best (most harmoniously) with people of other positive signs. However, soulmates of people with positive signs tend to have negative signs.
People of negative signs tend to be introvert, responsible, practical, serious and more likely to be pessimistic (when compared to people of positive signs). They typically relate better to people of other negative signs (though their soulmates are typically of positive signs).
The negative signs: Taurus, Cancer, Virgo, Scorpio, Capricorn, Pisces
Negative signs tend to relate best (most harmoniously) with people of other negative signs. However, soulmates of people with negative signs tend to have positive signs.
People of cardinal signs tend to be initiators and leaders, and are typically forceful and dynamic. On the negative side they can be seen as demanding, inconsiderate or controlling. Two cardinal signs together can have control issues.
The cardinal signs: Aries, Cancer, Libra, Capricorn
Generally people of cardinal signs have the most harmonius relationships with people of fixed or mutable signs, and don't do well with people of other cardinal signs. However, their soulmates tend to be of other cardinal signs.
People of fixed signs are known for their determination, deep thoughts and persistence. They tend to achieve more than the other (cardinal or mutable) signs due to being so willful. On the negative side they can be stubborn, opinionated and inflexible.
The fixed signs: Taurus, Leo, Scorpio, Aquarius
Generally people of fixed signs have the most harmonius relationships with people of cardinal or mutable signs, and don't do well with people of other fixed signs. However, their soulmates tend to be of other fixed signs.
People of mutable signs tend to be the most flexible and adaptable to change. They don't feel the urge to constantly create change (like cardinal signs do) or to constantly stick with a viewpoint (like fixed signs do). They're a healthy balance of the two extremes. On the negative side they can be seen as indecisive or flighty by those of fixed or cardinal signs.
The mutable signs: Gemini, Virgo,Sagittarius, Pisces
Generally people of mutable signs have the most harmonius relationships with people of fixed or cardinal signs, and don't do well with people of other mutable signs. However, their soulmates tend to be of other mutable signs.
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Articles answering questions related to more specific areas of astrology compatibility.
Astrology and soulmates
Astrology and seduction
Astrology and religion
Astrology and astronomy
Astrology and birth
Does astrology work?
How does astrology work?
Astrology birth charts
Ophiuchus the 13th sign
Have a question which isn't covered? Please feel free to Ask an astrology question.
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