Seven is such an arbitrary number.
There are seven days in the week. Why? Well, because either the Babylonians or the Hebrews, or possibly both independently, decided that something that’s close to (but not quite) a quarter of a moon was helpful.
There are seven luminaries in the sky, the “classical planets,” all the traveling stars that didn’t stay still: the sun, the moon, Mercury, Venus, Mars, Jupiter, and Saturn. (They also lent their names to the days of the week.) Why seven? Well, because Uranus and Neptune are too far away to be seen by the naked eye.
There are seven colors in the rainbow. Why? Because Isaac Newton was very religious, and very into numerology, so he declared that “indigo” was a separate color, to make seven.
There are seven seas. What are they? Well, they are
- the Arctic Ocean, the North Atlantic Ocean, the South Atlantic Ocean, the Indian Ocean, the North Pacific Ocean, the South Pacific Ocean, and the Southern Ocean
- the Persian Gulf, the Arabian Sea, the Bay of Bengal, the Strait of Malacca, the Singapore Strait, the Gulf of Thailand, and the South China Sea
- the Adriatic Sea, the Mediterranean Sea, the Black Sea, the Caspian Sea, the Persian Gulf, the Arabian Sea, and the Red Sea
- the Sea of Galilee, the Dead Sea, the Red Sea, Birkat Ram, Lake Hula, the Sea of Aspamia, and the Mediterranean Sea.
- So, not arbitrary at all. No way.
There are seven continents, so long as you count Europe and Asia as separate, and also North and South America as separate, which people in many countries do not.
There are seven notes in the traditional western diatonic scale. Okay, this one isn’t quite arbitrary. It turns out there is a lot of mathematics involved. And it’s by far the most aesthetically pleasing scale to western ears. But which came first? Do we find it pleasing because it’s what we’re used to? Or did we adopt it because it was pleasing?
There were seven wonders of the ancient world. Why seven? Because the Greeks liked that number.
Sevens abound in scripture, particularly the Hebrew Bible and the New Testament. Why? Because seven is a holy number. Why is seven a holy number? Because it abounds in scripture.
Seriously, seven? You’re a squatter. You just show up wherever other numbers haven’t yet been, and say, “This is mine.” No wonder seven is loaded with such symbolism and superstition.