The four noble persons
Four milestones on the road to freedom, each marked by which inner chains a person has permanently snapped.
Awakening in early Buddhism is not pictured as a single all-or-nothing flash but as a road with measurable milestones. The four noble persons (Pali ariya-puggala, "noble individuals") are the four kinds of person defined by how far they have traveled — specifically, by which of the mind's binding habits, called "fetters," they have permanently cut. "Noble" here simply means someone who has had a first genuine, irreversible glimpse of the truth, not someone of high birth.
The four, in ascending order, are: (1) the stream-enterer (sotāpanna) — one who has cut the first three fetters: the view of a fixed personal self (the deep-seated assumption "I am a solid, separate entity"), doubt about the path, and clinging to rules and rituals as ends in themselves — and is now certain to reach full liberation within at most seven more lives; (2) the once-returner (sakadāgāmī) — who has additionally weakened greed and ill will and will be reborn in this kind of world at most once more; (3) the non-returner (anāgāmī) — who has uprooted sensual desire and ill will entirely and will not be reborn into the sense-world again; and (4) the arhat (arahant, "worthy one") — who has severed all ten fetters, including the subtlest residue of self-conceit (the bare felt sense "I am"), restlessness, and ignorance, and is fully free, with no more rebirth.
Note that cutting the first fetter is not yet the complete uprooting of self-clinging: the stream-enterer is free of the wrong view of a self, but the faint conceit "I am" lingers until arhatship. The value of this scheme is that it makes the path concrete and gradual — liberation is a sequence of definite, irreversible steps rather than a vague aspiration — and it keeps the goal grounded, since progress is measured by what unwholesome habits actually fall away, not by visions or powers.