The five aggregates (khandhas) are form, feeling, perception, volitional formations, and consciousness. They are not five pieces assembled around a hidden soul. They are five categories for examining everything that is ordinarily taken as "I" and "mine." When appropriated, they are called the five aggregates subject to clinging and summarized as dukkha in the first noble truth.
Form includes the physical body and materiality. Feeling is pleasant, painful, or neutral tone. Perception recognizes and marks features—red, loud, familiar, dangerous. Volitional formations include intentions and many constructed mental activities. Consciousness is awareness dependent on a sense faculty and its object: eye-consciousness, ear-consciousness, mind-consciousness, and so on. It is not presented as an independent eternal witness.
In the Discourse on the Characteristic of Not-Self (SN 22.59), the Buddha asks whether each aggregate is permanent or impermanent, easeful or stressful under change, and fit to be regarded as mine, I, or self. He also points to lack of mastery: if form were self, one could command it never to become ill or change. The same applies to feeling, perception, formations, and consciousness.
The conclusion is a disciplined way of seeing: any form, feeling, perception, formation, or consciousness—past, future, or present; internal or external; coarse or subtle; inferior or superior; far or near—is seen as "not mine, not I, not my self." This is not a mantra for dissociation. It follows ethical training and collectedness, and it is directed toward relinquishing clinging.
Conventional language remains usable. The Buddha says "I" and addresses people by name. Not-self does not cancel promises, compassion, or kamma. It prevents conventional identity from being mistaken for an unchanging essence capable of ownership and control.
Soon after the first discourse, the Buddha guides the five monks through each aggregate. They agree that what is impermanent, afflicted, and subject to change is not fit to be treated as permanent self. During the teaching, their minds are freed through non-clinging.
The monk Khemaka no longer identifies any aggregate as self, yet admits a subtle residual sense of "I am" associated with the five aggregates. Through discussion with other monks, both he and his listeners deepen insight and are freed.