Empedocles, a fifth century BCE Greek philosopher, originated the terms Fire, Earth, Air, and Water. He explained the nature of the universe as an interaction of two opposing principles called love and strife manipulating the four elements. He stated that these four elements were all equal, of the same age, that each rules its own province, and each possesses its own individual character. Different mixtures of these elements produced the different natures of things. Empedocles said that those who have near equal proportions of the four elements are more intelligent and have the most exact perceptions.
Each sign is associated one of the classical elements (water, fire, earth and air.)  Fire and Air signs are considered positive or extrovert, masculine signs; while Water and Earth signs are considered negative, introvert, feminine signs.
Aries, Leo, and Sagittarius—fire elements: The Fire signs exhibit righteousness. These people conform to the standard of moral law. They do what is right and are known for their sense of fair play. They are truthful, straight-forward, just, upright and virtuous in their dealings with other people. They demonstrate courage, fortitude, zeal and pugnacity. They have the mental and moral strength that enables them to venture into unknown waters and to persevere and withstand danger. They are confident in their actions. They have mettle, resolution, and tenacity. They will fight for their principles and have a stubborn persistence that is unwilling to recognize defeat. They are willing to keep fighting under all odds. They are aggressive and thrive on challenge. The Fire signs are of a spiritual nature. Their essential characteristic qualities are liveliness, energy, ardor, enthusiasm, courage and action. They have a firm, courageous and assertive disposition which is their most characteristic quality. The emotional nature of the Fire sign is goal oriented. These people like to win or be the best in anything they pursue. Their aggressive nature makes them just one big ego. There is nothing more stimulating to them than to win, and there is nothing more depressing to their ego than to lose. They strive to be the center of attention and are at home when showing off. They are straight-forward and have no reservations about hurting the feelings of others by their forthrightness. The main virtue of this sign is being just and right.
Taurus, Virgo, and Capricorn—earth elements: The Earth signs show propriety. They are conventional, proper and fitting. They follow what is socially acceptable in conduct, behavior and speech. They have excellent manners and are very polite. They are prudent and have a deep regard for conventional rules of behavior. The Earth signs by nature are merchants. They are the storekeepers, barterers and traders. They are at their best when buying or selling material or tangible commodities. Most are very business oriented. The Earth signs have a physical nature. They have a characteristic love for the material, tangible things. They derive pleasure from sensory stimulation such as taste, smell and feel. They surround themselves with tangible and material items such as fine furniture, art and jewelry; most have a nice home that is meticulous and expertly decorated. They have good taste in clothing and most are connoisseurs of food and drink. The Earth signs' emotions are aroused by sensory stimulation. Each of the five senses can produce an emotional response. Sight, sound, touch, smell and taste brings both joy or depression. Nice peaceful surroundings, lively music, quality crafted materials, pleasant smelling tasty foods as well as financial security are all conditions required for an emotionally happy stable Earth sign. Earth signs are normally not prone to physical violence, however, as in any situation.
Gemini, Libra, and Aquarius—air elements: The Air signs possess the virtue of knowledge. This does not mean they are more intelligent than anyone else but are generally well-rounded and informed. They are good communicators. Most have a good grasp of the language and generally know a little something about everything - they can communicate well on any subject under discussion because they are so well-read and learned. They have good personalities and are easy to get to know. The Air signs are what the philosophers called seers or priests. These are mentally inclined people. They actively acquire knowledge through experience, education and association. The Air signs are curious, original, well-disciplined, quick thinking, and possess initiative. They are rational in their methods, rather than depending upon emotional or physical factors. They enjoy any type of entertainment where they can use their intellectual capacity, and their ability to think quickly and accurately often gives them the upper hand. The emotional nature of the Air signs is directed toward self appraisal. Air signs have a tendency to judge themselves harshly. They set standards for themselves when its comes to their hygiene, fashion, education, job performance, and family. At their worst, they can be mean. They carry a grudge, and are quick to express their opinion. Libra is not as violent as Aquarius or Gemini. Aquarius is known to change their temper like a change in wind direction. The Air signs will not hesitate one moment to express their anger verbally, but physical violence is not a first choice during that anger.
Cancer, Scorpio, and Pisces—water elements: Torrents of passion well within water signs and they feel things deeply. However, water signs are always emotionally reserved, no matter what impression they might give on the surface. Still water, it has been said, runs deep, and the mystery about water pertains to this group (especially Scorpio). A water sign will always become quiet or withdrawn when they are trying to sort things out. It will take some time to get to know them well, for they reveal themselves slowly. They realize their intense emotions hold tremendous power, and they tend to handle their feelings carefully. When they fall in love, water signs love with their whole hearts and all their devotion. Their sensitivity makes them highly aggressive, even low-self esteemed as the Pisces. Often psychic, water signs read your true intentions simply by reading your gestures and body language and will trust actions more than words (Pisces, particularly, has elevated this talent to a high art). This is a highly imaginative group and very creative. Their observations on the human condition often inspire masterpieces of painting, music, photography, literature, or dance. Working in studios or small self-employed businesses (usually connected to the creative arts) appeals to water signs. Their right-on-target intuition makes them succeed in financial areas too.
The Three Qualities
The Qualities assign the Signs into Quadruplicities, three groups of four. They are occasionally referred to as crosses because each quality forms a cross when drawn across the zodiac. Christian astrology relates the three qualities to the three aspects of God in the trinity.
Cardinal signs (Aries, Cancer, Libra and Capricorn) are associated with initiation, creativity and leadership.
Fixed signs (Taurus, Leo, Scorpio and Aquarius) are associated with stabilization, determination, depth and persistence.
Mutable signs (Gemini, Virgo, Sagittarius and Pisces) are associated with adaptability, service-providing and expansion.