Why The Number 7 Is Considered Good Luck

Luck is a strange thing. By definition, it's a random and uncontrollable phenomenon, and yet some believe it can be guided or invoked. It's also an attribute or action. For example, an object — some charm, perhaps —  is lucky, or a prescribed behavior like walking under a ladder is unlucky. When considered rationally, belief in "luck" seems like a weird and atavistic holdover from the days when our ancestors peered into the sky and hoped its gods would deliver rain. Attempts to configure, arrange, or manipulate luck are indistinguishable from ritual or folk magick, whether folks realize it or not.

So why, oh why, would a number be lucky? A number isn't a thing. A number isn't an action. A number is what kindergarteners say when counting apples. It's a mathematical quantification of a discrete amount of visible objects, or a numerical description of relationships between the properties of physical objects. And seven, in particular, seems to come up again and again as "lucky" around the entire world. In China, the number seven is a mystical number representing harmony between the elements. Indian astrology likewise considers the number seven to be related to mysticism and spiritual matters. And of course, there are all the callouts to the number seven in the Bible. But why? Maybe it's reasonable to assume that the number seven is considered lucky because it's linked to a variety of historically, textually, and culturally auspicious sources. There's also a possible scientific basis.

Maybe it's reasonable to assume that the number seven is considered lucky because it's linked to a variety of historically, textually, and culturally auspicious sources. The Greek myth about the Pleiades constellation (seen above), or "seven sisters," recounts how Zeus transformed the daughters of Atlas — the Titan who supports Earth on his shoulders — into stars to protect them from being raped. But this tale goes back much farther than Classical Athens some 2,500 years ago. Versions of it show up in various societies, such as Native American, Asian, and African, indicating that some original version existed before those peoples split. According to The Conversation, this puts the tale at about 100,000 years old.

As mentioned, we've also got the much more recent Biblical stories about God making the world in seven days, or Jesus performing seven miracles on the Sabbath, or seven churches described in Revelation. In Islam, hajj pilgrims in Mecca walk around the Kabba seven times. Hinduism describes seven steps along the path to enlightenment. Then there are cutesy factoids like the visible light spectrum containing seven visible colors, and the seven modes of diatonic music scales having seven unique tones each.

However, readers ought to be aware of the ultra-obvious and well-known human tendency to draw meaningful connections between even the most spurious and illogical points, defined by psychologists as apophenia. True to apophenia, believers will likely say that seven's lucky properties inspired our stories of its power — not the other way around.

Ultimately, seven's supposedly lucky properties may derive from the most dispassionate of causes: mathematics and neurology. In a story dating back to July 7, 2007 — 7/7/07 — NPR chatted with Stanford University's Keith Devlin about the "magic" of the number seven. Yes, there are nifty mathematical tricks involving this number — multiplying, dividing, squaring, square rooting, etc. But more pointedly, humans bump up against an innate cognitive counting ceiling of "seven" when trying to capture objects in our field of view, which itself relates to verbal counting ability. A study in Psychological Science discusses this in depth. Similarly, psychologists have long held that "seven plus or minus two" — sometimes disputed — is the number of items that humans can store in working memory, as a study in Psychological Review outlines. Perhaps humanity is just neurologically keyed to quantities of seven, and our limitation somehow manifests in our stories and beliefs.

That being said, the natural world plays a role in relating some special property of seven. As Discover Magazine points out, for example, ancient Babylonians looked to the seven prominent celestial bodies in the sky — sun, the moon, Mercury, Venus, Mars, Jupiter, and Saturn — and from this devised their seven-day week, which we still use to this day. At minimum, seven's true luck is how it has kept its significance for thousands of years.