Take pi (3.14159...) and raise it to the fourth power; then add that to the value of pi raised to the fifth power. The total (403.428...) is exceedingly close to e (2.71828...) raised to the sixth power. Coincidence? Sure, in the sense that two things have "coincided", i.e., come together. But what kind of coincidence is this?

About 15 years ago a friend (JB) and I tried to come up with a taxonomy of coincidences — or at least some useful categories to describe such things. We never finished or properly wrote it up ... but as an interim snapshot, here are some examples of our system:

• Mere coincidence — a purely accidental alignment of objects, like some of the constellations of stars in the sky
• Definitional coincidence — a match that comes because something was arbitrarily set that way, like the precise ratio (2.54) between centimeters and inches
• Suggestive coincidence — a relationship that points to something more significant, like the jigsaw-puzzle fit between Africa and South America
• Causal coincidence — a pattern that emerges because one part influences, triggers, or leads to another
• Transient coincidence — a temporary linkage among otherwise unrelated objects or values
• Deep coincidence — a subtle, nonobvious connection among apparently disparate things

Of course, what's "deep" to one observer may be transparently obvious to another. Over time, a coincidence may shift from one class to another, as people understand it better. And some coincidences may belong in multiple bins, depending on how they're viewed or analyzed.

So what other categories of coincidence should be added to the above? (see CorrelationsAndCausality and CoincidentalTaxonomy2)

TopicScience - 2001-10-19

--—
Hmmm. Coincidence may be that we don't yet understand the correlation. I am suspicious of a greater piece of unknown information whenever I hear the word coincidence. Take the randomness of galaxies, stars. I see solar systems as big atoms and infinity as more about size than time. Judy Decker

Many years ago I read The Roots of Coinsidence by Aldous Huxley. It gave me pause to think about what we call the "real" or physical world and what it's made of. Then I stubbed my toe and came back to my senses.

(correlates: PaulHolbrook, PartyLines, QuarterJinx, ...)