古代西方哲学家认为构成自然界的物体并衍生万物的物质是水、火、地、风四大元素。地球依着黄道运行其实就是四大元素的流转变化，因此将黄道12星座分为四类。

There are two classifications of the Signs of the Zodiac -- Elements and Qualities--and they each refer to core human characteristics. The Elements, which are also known as Triplicities (as in groupings of three), speak to the basic nature and temperament of a Sign, whereas Qualities address their manner of expression.
The Elements (Fire, Earth, Air and Water) are based on ancient Greek philosophy. The ancients took it back to square one, the building blocks of life: the solid earth upon which we stand, the running water we use as a resource, the air we breathe and the fire which keeps us warm and aids in the creation of additional resources. It's easy to see a kinship to science in this elemental plan.

With the individual in mind, the Greeks started philosophizing a bit. In this scenario, the body is considered earthy, feelings are fluid, thoughts often airy and activity animated and energetic. As Astrology developed, the ancients attached these elemental characteristics to the Signs, seeing as how it made sense to place a watery label on a more emotional sort. Thus evolved the classification of the Signs to their corresponding Elements.

The four Elements and their corresponding Signs are Fire (Aries, Leo and Sagittarius), Earth (Taurus, Virgo and Capricorn), Air (Gemini, Libra and Aquarius) and Water (Cancer, Scorpio, and Pisces). While the Elements in and of themselves help to describe our basic nature, once combined in our overall astrological chart, they help to define us as a whole and complex person.

In looking at an individual's astrological chart, the presence of more Fire Signs may well indicate a fiery, combustible personality. Along the same lines, the absence of Earth Signs would indicate someone who is not very grounded or practical. The presence of a mix of all of the Elements would be a sign of a well-rounded individual. 中文大意：
本位、固定和变动的三分法是各星座行为举止的反映；而古希腊哲学体系从自然因素出发，把12星座按生命原理分为四类：即稳固的“地”相星座，宁静的“水”相星座，灵活的“风”相星座和激情的“火”相星座。在这些先哲们的眼中，人是拥有坚实身板、复杂情感、多变的想法和旺盛的精力的生命个体。随着占星术的发展，这些最基础的因素被运用于星座学中，更多地体现了人的情感特征。
按照四分法，火相星座包括白羊、狮子和射手座；地相星座包括金牛、处女和魔羯座；风相星座包括双子、天秤和水瓶座；水相星座则涵盖巨蟹、天蝎和双鱼座。不同的自然特质反映了各类星座不同的天然禀性。火相星座的人精力充沛，感情奔放激烈，有十足的行动力，但来的快去的也快，有时较草率和粗心。地相星座的人慎重、冷静，对待感情真诚持久，做事也脚踏实地，但有时过于保守和自信心不强。风相星座的人思维发达，想象力丰富，有思想家的倾向，擅长社交，语言表达能力强，但性格变化多端，有喜新厌旧和情绪化的毛病。水相星座的人温柔宁静、感情细腻，对事物的洞察力极强，直觉也很敏感，但有时想法不切实际且喜凭感情用事。搞清楚各类星座的特点，有助于我们全面地了解一个复杂的人。