The equilateral triangle (as well as the single-axis
symmetric triangle, ) is earlier than , , , and , but older than, for example, the pentagram and the
swastika. seems hardly to have been used in the
prehistoric age, i.e. it is neither seen on the oldest rock carvings
nor in cave paintings.
is first and foremost associated with the holy, divine number of 3. It is through the tension of opposites that the new is created, the third. Philosophically, the thesis gives rise to its antithesis, and these two together create a synthesis (Hegel). When Marx had worked upon this Hegelian idea it became dialectical materialism, further developped by chairman Mao. Graphically, we can exemplify it with the opposites and , which when synthesized become . Xenocrate, who died in 324 B.C., stated that was a symbol for God. In Christian symbolism it stands for the Holy Trinity.
is also a symbol for power and, as such, related to danger. But according to the law of the polarity of meanings of the elementary graphs, it also means safety and also sometimes success and prosperity. The Hittites used it to mean well, good, or healthy.
As is often the case with basic gestalts the two meanings are sometimes united in the same sign occurrence. This is so when is used as a traffic sign, where it indicates danger or a threat, but also safety for some of those who observe the sign. One example of this is the traffic sign for pedestrian crossing, a square (representing the ground), with a triangle in it (for danger or safety) in which one sees the markings of a pedestrian crossing, and a stylized picture of a walking man. For car drivers this traffic sign means danger, pedestrians ahead. But for the pedestrians it means safety: "Here we can cross the street safely."
is used as a standard sign on the dashboard of cars for the push-button for warning lights. It also appears as a warning triangle to be folded out and placed on the road when a car is stopped on a highway. On medicine packaging means a drug that can slow down reactions.
In astrology represents the most positive of the aspects, the trine, or the angle of 120 degrees between planets, but it is also used to represent the astrological element of fire, the fire signs.
The astrological elements are organized in the so-called triplicities, a dividing of the zodiac signs into four groups of three signs: fire signs, ; earth signs, ; air signs, ; and water signs, . The fire signs are Aries, ; Leo, ; and Sagittarius, .
The astrological elements are symbols for four different ways of relating to and understanding the world the individual lives in. Individuals mainly influenced by the element of fire relate to people and things in terms of the opportunities these might mean for themselves and their lives. Signs that belong to the same element lie in the aspect , trine, to one another. This creates a basis for harmony, approachability, and understanding. According to the trend in modern astrology toward Jungian psychoanalysis, one or more of these perceptionary elements are dominant in an individual, while the others are linked to the subconscious complex called the shadow, a person of the same sex characterized by despicable and contemptuous qualities. The shadow is often symbolized by Saturn, , in the birth chart. The other most important complex of this type is animus, an ideal personality of the opposite sex that is subconsciously projected onto suitable persons of the opposite sex, leading to love affairs of the type, "it is as if we had known each other all our lives although we met just a week ago". Both in Tibet and in European alchemy signified the element of fire. With a line added, as in or , it was transformed into the alchemical symbol for the element of air. (See below for a similar change of meaning.)
is used in some 40 modern ideographic systems. It is used in the ground-to-air emergency code to mean it is probably safe to land here. In botany it means evergreen perennials. It appears as a tele-engineering sign for telephone and in meteorology can signify hail. Philatelists use it to indicate that enough of the envelope is left to show the whole postmark together with the stamp. It is used in physics to indicate a lowering of the freezing point or a lowering of the temperature. Chemists, however, use it to mean warming up (as did the alchemists). In cartography sometimes stands for natural gas, while in the same context can stand for oil or oil well, all these denotations connected to the element of fire.