You can’t step in the same river twice. Here’s a fun mental exercise.
Imagine standing in a river for a moment. Water is flowing around your feet. You are standing still, but a few seconds later you’re touching completely different water. The river has the same name, it’s in the same place, and everyone still points at it and calls it the same thing, but the water that made up that exact moment is already gone and replaced by new water.
That’s the basic idea: when you come back, the river has changed.
And so have you.
The idea is usually associated with the Greek philosopher Heraclitus. You may have seen the longer version online: “It’s not the same river and he’s not the same man.” That captures the idea pretty well, but it is a modern paraphrase rather than a surviving word-for-word quote from Heraclitus (Graham, 2023).
Everything is in motion
Heraclitus is often associated with flux: the idea that change is built into the way the world works. Exactly how radical his theory of flux was is still debated, because apparently we have managed to argue about a river for more than 2,000 years (Graham, 2023).
Things move from one state into another. Day becomes night. Heat becomes cold. A seed becomes a tree. The river keeps flowing. A lot of this becomes easier to notice when you look at opposites: light and dark, hot and cold. Yin and Yang is another familiar image of opposites, although that comes from a completely different philosophical tradition.
You notice night because there was day before it. You notice cold because you remember warmth. One state leads to another, and suddenly you can see (or feel) the change happening.
The river just makes the whole thing easier to notice.
You’re changing too
What makes this idea more interesting is that there is another change constantly happening.
You are changing too.
Think about it: you are never exactly in the same state twice. You learn things, forget things, change your mind, get tired, get excited, eat, make decisions, regret some of them, and experience new things.
So even if you somehow managed to return to the exact same spot in the exact same river, at the exact same time of day, you still wouldn’t be the same person.
That version of you already moved downstream too.
Same name, different moment
This is the part I like. We keep giving things the same name even when they are constantly changing.
The river is still “the river.”
You are still “you.”
Your city is still your city even after buildings disappear and new ones emerge.
Apparently we are very comfortable with continuity as long as the change happens slowly enough.
And if you want to go deeper into the rabbit hole, philosophers found a way to make it worse by replacing the river with a boat and changing every plank one by one.
But that’s a story for another time.
The same river
So, in the sense of this mental exercise, you can’t really step into the same river twice. The next time you stand in the water, that water will be different. The moment will be different. You will be different.
Maybe only slightly.
Maybe completely.
But the version of the river you touched before is already gone, and so is the version of you who touched it.
Everything keeps moving.
That’s the point. Just keep swimming.
If you want to follow that invisible line into ritual and belief, continue with Why Your Brain Believes in Magic Even When You Don’t, or with the strange succession story of the Rex Nemorensis.
References
Graham, D. W. (2023). Heraclitus. In E. N. Zalta & U. Nodelman (Eds.), The Stanford Encyclopedia of Philosophy (Winter 2023 ed.). Metaphysics Research Lab, Stanford University. https://plato.stanford.edu/archives/win2023/entries/heraclitus/