The number two (2) symbolizes duality, or opposites: light and dark, hot and cold, dry and wet, male and female, divine and material (as in Cartesian dualism), Reichian sexuality and anxiety, and so on.
In the beginning was Two: the Sepher Yetzirah, or Book of Formation, (a Qabalistic text) states that all 22 Hebrew letters wanted to be the beginning of Creation, but the One God chose 'beit' (ב) - the second letter, (b) to begin Genesis 1:1 with the word 'bereisheet' ('in the beginning'). That sentence proclaimed a dualistic existence, "heaven and earth;" above and below, just as Hermes proclaimed in the Emerald Tablet. God then speaks light into existence and separates it from darkness; separates liquid from solid allowing land to emerge; separates Eve from Adam allowing humans to propagate; separates the wicked from the righteous with the deluge; etc.
Reichian Sexual Theory
It is also the marriage of opposites, as with the inflow and outflow of breathing (a single function), the contraction and expansion of the heart, indeed most all biological processes.
Wilhelm Reich, a student of Freud, theorized based on Hegel's dialectic (thesis + antithesis = synthesis) that sexuality was fundamentally a similar phenomenon; his formula for sex was: Tension->Charge->Discharge->Relaxation. (See: Reich, The Bioelectrical Investigation of Sexuality and Anxiety.) He conceived of the idea of contraction-expansion as an archetypal principle, and -though science does not recognize it- his idea has been thoroughly confirmed: Respiratory, circulatory, digestive, homeostatic (e.g. thermoregulatory), excretory and muscular systems, as well as neuronal communication all reveal that this principle of contraction and expansion is ever-present.
The Nature of the Universe
Many religions, including Judaeo-Christianity and Zoroastrianism, believe that there is a constant war going on between the forces of good and of evil in this Universe, and that at the "end of time" there will be a final clash between God and Satan, Jesus and the Antichrist, and so on.
This is reflected on an individual level with the internal conflict of the animalistic and intellectual or higher self, the genital fixation that interferes with higher spiritual aspiration. These polarities of light and dark, genital and mental fixation, are also reflected in the sevenfold schema of Man and Nature with the Sun and Saturn, the pineal and root chakras, the lead and gold of alchemy (see: Seven). This article is a stub. Please help Symbolism Wiki by expanding it.