“The dark side” is the evil and malevolent aspect of human personality or society, often referred to in a lighthearted or comic context. The dark side is also, of course, the portion of Earth facing away from sunlight.
Figurative uses of the term go back hundreds of years, since it’s found in Christian imagery as well as such phrases as, “the dark side of life,” “the dark side of human nature,” “the dark side of the story,” and so on.
From a document titled Bruised Reed and Smoking Flax by Richard Sibbes, in 1620, comes, “These delight to be looking on the dark side of the cloud only,” in a discussion about human nature.
The phrase, however, became vastly more popular after the 1977 film Star Wars Episode IV: A New Hope, written and directed by George Lucas. Lucas portrayed the “dark side” as the evil aspect of the the underlying controlling power of the Universe (the Force). The Star Wars series demonstrated the classic good versus evil plots in Hollywood cowboy films. The “bad guy” in Star Wars was the Dark Jedi, Darth Vader, who went over the top in the black hat department.
The Pink Floyd album, Dark Side of the Moon, was released in 1973, when Star Wars was in production, and also became immensely popular. However, what is more likely than that album to have influenced Lucas’s concept was Jungian psychology’s model of the shadow aspect of personality, the unconscious or ‘dark’ side of personality.
From Carl Jung’s work Psychological Types, translated into English by H G Bayness and published in 1923: “For the sake of understanding, it is, I think, a good thing to detach the man from his shadow, the unconscious… One sees much in another man which does not belong to his conscious psychology, but which gleams out from his unconscious.”
And, in 1973, the US journal The Journal of Genetic Psychology published this: “The shadow is described as the dark side of the personality or representing the original conception of evil in the world. The latter conception places the shadow in the collective unconscious.”
Today, the use of “the dark side” in everyday language isn’t taken very seriously. It has the same linguistic weight as the phrase “be afraid, be very afraid,” which is never used in circumstances that are actually frightening .
“Come to the Dark Side” (often followed by “we have cookies”) is a popular Internet phrase, meant to be a tongue-in-cheek catchphrase.
There is the opposite aspect, as well. When I switched from a pc computer to an iMac, a friend congratulated me like this: “So glad to hear you’ve come over from the dark side!”