Whether you believe in rebirth or not, odds are you’ve either asked this question, or you’ve heard someone else ask it.
Rebirth makes sense in Hinduism, since Vedanta claims that there’s a soul or essence somewhere in the mind and body. When the body dies, this essence takes another based on its karma and desires.
Buddhism says the same thing, except there’s no soul or essence in the mind and body. There’s no us in us that’s driving the body-mind like a car. What we mistake for a self is actually self-interest, and what it’s pointing toward is bright, still, unbound selflessness. Like the center of a circle (unbound because the space inside and outside are both just space).
So, that being the case, wtf is reborn then? For that matter, what is it that’s born, lives, and dies in the first place?
Let’s say there are a bunch of trees, just growing in the woods, doing tree-stuff. Then someone chops them down to make a log cabin. Eventually, the wood rots and the cabin falls apart. Over hundreds of years, the wood slowly dissolves into soil where it becomes nutrients for other plants.
There was no self involved in any of that, but—at least on the surface—there was death and rebirth. The trees died and were reborn as a cabin. The cabin “died” and was reborn as rotting logs. The logs “died” and became reborn as soil, and the soil was reborn as new plants.
There’s no self in that because nothing really even happened. A tree is a bunch of fibers, as is a log cabin. When the wood started to rot, those fibers separated from each other, and then each one was woven with other fibers. Throughout all of that, nothing was actually created or destroyed.
Really, the body is just like that tree, a bundle of fibers. As time goes on, they start to loosen and fray until they come apart. But none of them disappear. They’re all sewn into other cloths.
For early Buddhists, only the self was empty. The body and mental processes weren’t. So the same way that the body is unwound and sewn into other things, mental processes are too.
Some Buddhists believed that only consciousness was passed on, others that it was volition and consciousness. A few thought that the whole package (feelings, perception, volition, and consciousness) was delivered to another body.
If we use the body as an example, the most likely chain of events would be dispersion. Your feelings might go to a kitten in Nepal, your perception to a bear in Alaska, your habits to a kid in France, and consciousness to a bumblebee in Idaho, each aggregate drawn here and there by karma.
Middle Buddhists, like Nagarjuna, disagreed with this. He didn’t say it was unreal, but that it was a mind trick. Because if we examine each of these things the same way we did the body and mind in general, we find that there’s no feeling within feeling, no perception in perception, no volition in volition, or consciousness in consciousness.
Basically, no fiber in the fiber. Nothing exists in itself, for itself, or by itself. By Nagarjuna’s reckoning, there’s no such thing as birth, life, death, and rebirth in actuality.
Early Buddhism takes away the self, middle Buddhism takes away the surroundings too. Everything’s just an appearance, like a mirage. Mirages come and go, sure, he acknowledged that, but it’s still just a mirage—that’s why it comes and goes.
His predecessors got kinda carried away with this after he died, and the whole thing got too nihilistic. So, the mind-only and Buddha-nature schools came around to lighten things up.
For the mind-only school, things were only empty of separation, and even though they were empty of being individual selves, they were full of Mind, and this emptiness was the nature of Mind.
For Buddha-nature, emptiness isn’t dead absence or non-existence. It’s bright and shining and clear. It’s present.
Zen considers itself the One Vehicle, meaning it uses and casts aside all of the aforementioned views as needed, but its heart is Buddha-nature which it blended with the Tao.
In the West, most of us don’t believe in metaphysical karma or rebirth, neither as an illusion or actuality. Karma has been appropriated into psychology and sociology, and rebirth is a metaphor for moment-to-moment impermanence.
A lot of Western Buddhists have let the self or ego creep back into the picture, though. There’s an annihilationist (meaning that when we die, we’re dead) streak a mile wide. There’s also an ascetic trend that’s focused on giving up the self or ego.
Siddhartha called these wrongs views, because anatta means there’s no self or ego to die or give up, and no self that arises from or in the body and mind. There’s no I-aggregate.
In Zen, not-self isn’t a simple absence, it’s the True Self. Birthless, deathless, and indescribable. This is 100% in line with the early teachings, and the words Zennies use to describe this Not-Self, are the same ones Buddha used to describe Nirvana. Hence the optimistic line in the Heart Sutra:
Nirvana is already here.