Look at anything long enough, the tradition says, and three characteristics come into focus. Not three beliefs to adopt: three things to check. Buddhism calls them the Tilakkhana, the three marks of existence, and holds that they are stamped on everything that arises from causes, which is everything you will ever experience. Everything changes. Nothing that changes can finally satisfy. And nowhere in any of it can a fixed, separate self be found.
The Dhammapada, the tradition's most-quoted collection of verses, presents the marks in exactly this spirit. Three verses in a row each open with one mark and end on the same refrain: when one sees this with wisdom, one turns away from suffering; this is the path to purification. Not "when one believes this". The marks are not a creed. They are instructions for where to look, and the seeing itself is the path.
Everything changes — Anicca
The first mark, anicca, impermanence, is the easiest to state and the hardest to live as if it were true. Everything that arises passes: seasons, moods, bodies, friendships, civilisations, the thought you are having right now. Nothing you can point to holds still, including the one doing the pointing.
The insight is not Buddhism's private property. Heraclitus, watching a river in Greece around the same century, saw that you cannot step into the same river twice; the two sightings are set side by side on Death and impermanence, which is also where impermanence becomes a practice rather than a fact, down to maranasati, mindfulness of death. Here the mark itself is enough: change is not something that occasionally happens to things. Change is what things are doing, all the time. Permanence was the story; flux is the observation.
Nothing fully satisfies — Dukkha
The second mark follows from the first the way an ache follows a bad footing. If everything changes, then everything you lean on is moving under your weight, and dukkha, usually translated suffering or unsatisfactoriness, is what leaning on moving things feels like. Especially the pleasant ones, because those are the ones you lean on hardest.
As a mark, dukkha is not the claim that life is misery. It is the quieter observation that nothing depending on conditions can deliver the settled satisfaction the mind expects of it, because the conditions are already shifting. The full diagnosis, cause and treatment included, is the work of the four noble truths; here it is enough to see how the marks connect. The second is what the first feels like from inside a mind that has not yet accepted it.
No fixed self — Anatta
The third mark looks inward, and it is the subtlest. Search experience for the experiencer, the tradition says, and you will not find a fixed, separate self standing behind it. You will find seeing, hearing, thinking, remembering, wanting: process all the way down, with no permanent someone operating the process. What we call "I" is real the way Heraclitus' river is real: a continuity of pattern, not a fixed thing underneath it. Why nothing stands alone or holds still is its own teaching, dependent origination.
The tradition even widens this mark beyond the other two: impermanence and unsatisfactoriness are stamped on everything that arises from conditions; non-self, the verses say, on all things without exception. It is the tradition's boldest cut, the one that most sharply divides it from yoga, and it gets its own section below.
The five skandhas
If there is no fixed self, what is actually here? The Buddha's answer is the five skandhas, the aggregates: five bundles of process that run together and get mistaken for an owner. Form (Rupa) is the body and the physical world it meets. Sensation (Vedana) is the immediate feel of each moment of contact: pleasant, unpleasant, neutral. Perception (Samjna) is the labelling that turns raw contact into "birdsong" or "threat". Mental formations (Sanskara) are the impulses, habits and intentions that push the mind around; yoga uses the same word for the grooves that repeated experience carves in the mind, a real kinship though not an exact match, and the yogic sense lives at Samskara and vasana. Consciousness (Vijnana) is the bare knowing of all of it.
An early nun, Vajirā, gave the teaching its most famous image. "Chariot" is a word we use when wheels, axle and frame are assembled a certain way; no chariot exists apart from the parts. "Self", she said, works the same way: a useful word for the aggregates running together, nothing extra standing behind them. The early discourses compress the whole teaching into one line: nothing whatsoever should be clung to as me or mine.
Two maps of what remains
Yoga examines the same layers and reports one thing more. Beneath every layer that changes, it says, there is Purusha: pure awareness, the still witness in which the changing layers appear. Not another layer, but the one thing that was never arising or passing at all. That witness has its own page at Purusha and Prakriti, and Buddhism declines it. Anatta does not say the witness is well hidden; it says no fixed witness is found, and that the search for one is the very reflex the teaching is trying to loosen.
This is a genuine difference, and this site keeps it: the honesty is worth more than the tidiness. Rest in the awareness that does not pass, says one. See that nothing needed to remain, says the other. What they share is the move that matters, the loosening of the grip on a small, defended self; the two accounts are held side by side on Death and impermanence, and in one line on The Convergence. You do not have to settle the question to practise. Both doors open off the same corridor.
Seeing is the path
The marks are not commandments, and not metaphysics to memorise: they are instruments. Three angles from which to look at any experience until it comes into focus. Insight meditation trains exactly this; Samatha & Vipassana describes stilling the water, then looking into precisely these three. It is also why the tradition counts delusion, taking the passing for permanent and the process for a person, as the root of the three poisons: the fog is, precisely, the marks unseen.
The Dhammapada's refrain keeps the emphasis where it belongs. Not: blessed are those who believe in impermanence. But: when one sees this with wisdom, one turns away from suffering. The marks hold whether or not anyone notices them, the tradition says; a Buddha only points. The difference the teaching makes begins the moment the looking does.