There is often a fourth Dharma Seal mentioned:
Together the three characteristics of existence are called ti-lakkhana in Pali or tri-laksana in Sanskrit.
By bringing the three (or four) seals into moment-to-moment experience through concentrated awareness, we are said to achieve wisdom – the third of the three higher trainings – the way out of samsara. Thus the method for leaving samsara involves a deep-rooted change in world view.
All compounded phenomena (things and experiences) are inconstant, unsteady, and impermanent. Everything we can experience through our senses is made up of parts, and its existence is dependent on external conditions. Everything is in constant flux, and so conditions and the thing itself is constantly changing. Things are constantly coming into being, and ceasing to be. Nothing lasts.
The important point here is that phenomena arise and cease according to (complex) conditions and not according to our whims and fancy. While we have limited ability to effect change to our possessions and surroundings, experience tells us that our feeble attempts are no guarantee that the results of our efforts will be to our liking. More often than not, the results fall short of our expectations.
In Mahayana Buddhism, a caveat is added: one should indeed always meditate on the impermanence and changefulness of compound structures and phenomena, but one must guard against extending this to the realm of Nirvana, where impermanence holds no sway and eternity alone obtains. To see Nirvana or the Buddha (in his ultimate Dharmakaya nature) as impermanent would be to indulge in "perverted Dharma" and would be to go seriously astray, according to late Mahayana doctrines attributed to the Buddha. Other schools of Buddhism, however, feel uneasy about this teaching.
Striving for what we desire, we may experience stress and suffering – dukkha. Getting what we desired, we may find delight and happiness. Soon after, the novelty may wear out and we may get bored with it. Boredom is a form of dissatisfaction (or suffering) and to escape from it, we divert ourselves from such boredom by indulging in a pursuit of new forms of pleasure. Sometimes not willing to relinquish objects that we are already uninterested in, we start to collect and amass possessions instead of sharing with others who may have better uses for them than we do. Boredom is a result of change: the change of our interest in that object of desire which so captivated us in the first place.
If we do not get bored already, then change may instead occur in the object of desire. Silverware may become tarnished, a new dress worn thin or a gadget gone obsolete. Or it may become broken, causing us to grieve. In some cases it may get lost or stolen. In some cases, we may worry about such losses even before they happen. Husbands and wives worry about losing their spouses even though their partners are faithful. Unfortunately, sometimes our very worry and fear drives us to act irrationally, resulting in distrust and breaking up of the very relationship that we cherished so much.
While we like changes such as becoming an adult when we are in our teens, we dislike the change called aging. While we strive for change to become rich, we fear the change of retrenchment. We are selective in our attitude towards the transient nature of our very existence. Unfortunately, this transient nature is unselective. We can try to fight it, just as many have tried since beginningless time, only to have our efforts washed away through the passages of time. As a result, we continually experience dissatisfaction or suffering due to the very impermanence of compounded phenomena.
Only in the realm of Nirvana – so Buddhism insists — can true and lasting happiness be found. Nirvana is the opposite of the conditional, the transitory and the painful, so it does not result in disappointment or deterioration of the state of bliss. Nirvana is the refuge from the otherwise universal tyranny of change and suffering. In other schools of Buddhism, nirvana is not viewed as the goal, but merely as a projection from the state of samsara. According to these schools samsara (daily routine) and nirvana (perfection) are two sides of the same coin.
In Indian philosophy, the concept of a self is called ātman (that is, "soul" or metaphysical self), which refers to an unchanging, permanent essence conceived by virtue of existence. This concept and the related concept of Brahman, the Vedantic monistic ideal, which was regarded as an ultimate ātman for all beings, were indispensable for mainstream Indian metaphysics, logic, and science; for all apparent things there had to be an underlying and persistent reality, akin to a Platonic form. The Buddha rejected all concepts of ātman, emphasizing not permanence, but changeability. He taught that all concepts of a substantial personal self were incorrect, and formed in the realm of ignorance. The Buddha criticized conceiving theories even of a unitary soul or identity immanent in all things as unskillful in the Great Discourse on Causation. In fact, according to the Buddha's statement in Khandha Samyutta 47, all thoughts about self are necessarily, whether the thinker is aware of it or not, thoughts about the five aggregates or one of them.
A number of major Mahayana sutras (e.g. the Mahaparinirvana Sutra, the Tathagatagarbha Sutra, the Srimala Sutra, among others), the Buddha is presented as clarifying this teaching by saying that, while the skandhas (constituents of the ordinary body and mind) are not the self, there does truly exist an eternal, unchanging, blissful Buddha-essence in all sentient beings, which is the uncreated and deathless Buddha-nature ("Buddha-dhatu") or "True Self" of the Buddha himself. The "tathagatagarbha"/Buddha nature does not represent a substantial self; rather, it is a positive language expression of "sunyata" (emptiness) and represents the potentiality to realize Buddhahood through Buddhist practices; the intention of the teaching of tathagatagarbha (Buddha nature) is soteriological rather than theoretical.
This immaculate Buddhic Self (atman) is in no way to be construed as a mundane, impermanent, suffering "ego", of which it is the diametrical opposite. On the other hand, this Buddha-essence or Buddha-nature is also often explained as the potential for achieving Buddhahood, rather than an existing phenomenon one can grasp onto as being me or self. It is the opposite of a personalized, samsaric "I" or "mine". The paradox is that as soon as the Buddhist practitioner tries to grasp at this inner Buddha potency and cling to it as though it were his or her ego writ large, it proves elusive. It does not "exist" in the time-space conditioned and finite mode in which mundane things are bodied forth. It is presented by the Buddha in the relevant sutras as ultimately inexplicable, primordially present Reality itself – the living potency for Buddhahood inside all beings. It is finally revealed (in the last of the Buddha's Mahayana sutras, the Nirvana Sutra) not as the circumscribed "no self", the clinging ego (which is indeed anatta/anatman), but as the ever-enduring, egoless Great Self or Dharmakaya of the Buddha.
Anatta is discussed in the Questions of King Milinda, composed during the period of the Hellenistic Indo-Greek kingdom of the 2nd and 1st centuries BCE. In this text, the monk Nagasena demonstrates the concept of absolute "non-Self" by likening human beings to a chariot and challenges the Greek king "Milinda" (Menander) to find the essence of the chariot. Nagasena states that just as a chariot is made up of a number of things, none of which are the essence of the chariot in isolation, without the other pieces, similarly no one part of a person is a permanent entity; we can be broken up into five constituents – body, sensations, ideation, mental formations and consciousness – the consciousness being closest to the permanent idea of "Self", but is ever-changing with each new thought according to this viewpoint.
According to some thinkers both in the East and the West, the doctrine of "non-Self", may imply that Buddhism is a form of nihilism or something similar. However, as thinkers like Nagarjuna have clearly pointed out, Buddhism is not simply a rejection of the concept of existence or meaning, but of the hard and fast distinction between existence and non-existence, or rather between being and no-thingness. Phenomena are not independent from causes and conditions and do not exist as isolated things as we perceive them to be. The lack of a permanent, unchanging, substantial Self in beings and things does not mean that they do not experience growth and decay on the relative level. But on the ultimate level of analysis, one cannot distinguish an object from its causes and conditions or even distinguish between object and subject (an idea appearing relatively recently in Western science). Buddhism thus has much more in common with Western empiricism, pragmatism, anti-foundationalism, and even poststructuralism than with nihilism.
In the Nikāyas, the Buddha and his disciples commonly question or declare "Is that which is impermanent, subject to change, subject to suffering fit to be considered thus: 'This I am, this is mine, this is my self'?" The question which the Buddha poses to his audience is whether compounded phenomena are fit to be considered as self, to which the audience agrees that it is unworthy to be considered so. And in relinquishing such an attachment to compounded phenomena, such a person gives up delight, desire and craving for compounded phenomena and is unbounded by its change. When completely free from attachments, craving or desire to the five aggregates, such a person experiences then transcends the very causes of suffering.
In this way, the insight wisdom or prajñā of non-Self gives rise to cessation of suffering, and not an intellectual debate over whether a self exists or not.
It is by realizing (not merely understanding intellectually, but making real in one's experience) the three marks of conditioned existence that one develops prajñā, which is the antidote to the ignorance that lies at the root of all suffering. From the "tathagatagarbha-Mahayana" perspective (which diverges from the Theravadin understanding of Buddhism), however, a further step is required if full Buddhahood is to be attained: not only seeing what is impermanent, suffering and non-Self in the samsaric sphere, but equally recognising that which is truly Eternal, Blissful, Self, and Pure in the transcendental realm — the realm of Mahaparinirvana. The use of the term "Self" here is as defined in a manner specific to this genre of sutras; see Atman (Buddhism).
Some Buddhist traditions assert that Anatta pervades everything, and is not limited to personality, or soul. These traditions assert that Nirvana also has the quality of Anatta, but that Nirvana (by definition) is the cessation of Dukkha and Anicca.
In his Mulamadhyamakakarika (XXV:19), Nagarjuna says:
This verse points us to an interesting stress between dukkha and nirvana, through an argument based in anatta. This specific stress can be seen to be the key to (and possibly source for the development of) the deity yogas of vajrayana.
On the other hand, we are told that unconditioned, enlightened activity is not actually different from samsara.
At this level, the distinction between Sutra and Vajrayana remain that of view (departing vs. arriving), but basically the practitioner remains involved in undergoing a transformative development to his or her Weltanschauung, and in this context, these practices remain rooted in psychological change, grounded in the development of Samatha, or training in concentration.
However, there are certain practices in Tantra which are not solely concerned with psychological change; these revolve around the basic idea that it is possible to induce deep levels of concentration through psycho-physical methods as a result of special exercises. The purpose remains the same (to achieve liberating view), but the method involves a 'short cut' for the training in Samatha.