Anicca (Pali, Sanskrit, "impermanent " or "not enduring"), or Anitya (Sanskrit) is of the Three Marks of Existence in Buddhism. The teaching of the impermanence or transitorness of all things is central to the whole of Buddhist philosophy and practice. It involves the affirmation, as a truth statement, that all phenomena, both mental and physical, are without exception impermanent. Furthermore, despite this truth being everywhere evident and verifiable, people are in a state of ignorance regarding it. The transition from this ignorance to awareness (and personal acceptance) of the impermanence of all things constitutes…the Buddhist path of salvation, and this transition is effected by the aid of the Buddha and his teaching.
There are various ways in which anicca, or the impermanence of things, can be illustrated. Figuratively, the action of time is compared to a moving chariot wheel, which touches the ground one point at a time; an ever-flowing mountain stream, a bubble, a bouncing ball, or the sound of a bell. Introspectively one can verify the truth by observing that one's thoughts and feelings never remain the same but are in perpetual flux; that is, the extreme brevity of a single thought that never persists but always leads to another thought. Analytically, "impermanence" is to be observed in the fact that all things exists in dependence on something else, arise out of and become something else; no thing exists in isolation, no thing possesses stability. It is precisely in this respect that nibbana is to be understood as the antithesis of anicca, that is, as comprising duration, stability, and permanence, and why it is regarded worthy of personal aspiration, unlike the things of the world. The teaching on anicca links up with the Buddhist doctrine of "dependent origination," paticca-samuppada, which states that "all things have a beginning" and that "all things with a beginning must have an end"; the doctrine of anicca draws attention to the fact of their demise. The paramount importance of anicca in Buddhist teaching is spotlighted in the Buddha's last words, "decay is inherent in all things."
As a consequence of all of its focus of attention on impermanence, Buddhism teaches the practice of aniccanupassana, ("contemplation of impermanence" or Vipassana) as the way of learning the truth of impermanence. The importance of the practice of aniccanupassana has traditionally been demonstrated by the snapping of the fingers, this is an invaluable exercise illustrating how little attention people give to impermanence. The concern devoted to impermanence is not just an academic issue but is important to the process of continuity because it liberates the person from attachment to objects, both mental and physical, within the world. If things are impermanent they have no intrinsic value; therefore they are unworthy of one's preoccupation. In particular, emphasis is placed upon the impermanence of physical, emotional, and mental states through which the external world is perceived. The actual contemplation process involves observing, or watching, the rise or appearance of a certain datum, verifying its "dependent" or "caused" origin, then by a similar method, "watching" its subsidence or disappearance and verifying its transient characteristic. Here, a given object of experience, is not only "seen" to be impermanent but is also "deduced" to be such on the basis of the fact that it is "dependent" for its existence on something else which is impermanent; so, for example, "feeling" is impermanent because it is dependent on the "body" which is impermanent, and so on. It is a process by which one moves from the particular to the general and from the general back to the particular, until ultimately one arrives at the insight (panna) that all is "impermanent" (sabbam aniccam).
Acceding intellectually to the truth of impermanence is termed in Buddhism the acquisition of the "right view" and is synonymous with entry on the path to enlightenment. The discernment of impermanence correspondingly represents the "explosion" or "dissolution" of all wrong views because the construction of any metaphysical system necessarily rests upon the assumption of some notion of "permanence" or of some element of "permanence" within it; therefore, the acceptance of anicca works counter to the tendency to superimpose constructions on reality.
The Abhidhamma tradition sought to give an account and explanation of the mechanics of the empirical doctrine of anicca by suggesting physical theories of the precise lifespan or momentariness of things. And therefore, according to the Mahayana fell into the trap of developing a metaphysical theory about something whose very purpose was to exterminate such theories. The Mahayana, on the other hand, took the fact of the totality or universality of impermanence to imply the relativity of all things, an interpretation which contributed significantly to the design and formulation of its sunyata (emptiness or no-soul) doctrine. A.G.H.
Bowker, John, The Oxford Dictionary of World Religions, New York, Oxford University Press, 1997, pp. 70-71