The number four (4) symbolizes the material world: North, South, East and West, the 'four corners of the earth;' Earth, Air, Water and Fire, the constituents of the universe; and the four humors, the constituents of Man.
Venus is the fourth classical planet, therefore it is fitting that her sign, the five-pointed star, shows 'the one' projecting upward beyond the material. (Five is symbolic of the Sacred Feminine and is associated with Venus for very good reason.) There are four stages in the alchemical process, though some fervently disagree. (See: C.G. Jung's Psychology and Alchemy.)
There are also 'four corners' in the year, being the equinoxes and solstices which constitute the four seasons (depending on where you live it may simply be 'wet' and 'dry', however).
The Gospels of Matthew, Mark, Luke and John reflect the idea of four being a 'foundation' for something higher (Christ).
In the Far East, however, particularly in China and Japan, number 4 carries a very distinct negative meaning, because the words "four" (四) and "death" (死) are pronounced exactly the same way (Pinyin: "sì", Japanese: "shi"). It is therefore considered an unlucky number (like 13 in the West) and some buildings even skip 4 in their floors numbering.
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