Buddha as the fundamental discipline admits the psychology and through it metaphysical problems are to be approached.
According to the perception of Buddha, the thought of human mind should shift from the absolute mind of metaphysical speculation to the human mind of psychological observation. The speculation and consciousness are the areas where the human thoughts and ideas appear. Nagasena considers the fact of continual change of human thought and ideas and dismisses the fact that the immortal soul is an illegitimate abstraction and reduces the self of man to a unified complex exhibiting an unbroken historical continuity. This belief affirms the negative position of the non-existence of the soul. The permanence of things is also denied.
According to the belief of Nagasena, there is no existence of soul. The word 'self' is cut down and only the states of self are spoken of. The self is considered as a stream of ideas. A common character is acquired by the several states of self and the abstraction of the common element is called the 'self' or 'Atman'. The Buddhist school of thought asserts the consciousness of self or the intuition of self, as a psychological impossibility. The scrutiny of a soul reveals the fact that certain qualities exist together. Soul is defined as the sum of the states that constitute the mental existence of human entity.
Nagasena perceives the distinction between thoughts and things. According to the perception of Nagarjuna, every individual possesses 'mana' and 'rupa' that are mind and body respectively. Neither body nor soul is permanent element. The ideas, states and modifications are temporary. Though the human entity perceives that there is a permanent self that binds all the states of human being and preserves them all, but this assumption is not justified by actual experience. According to Hume, there is nothing that can define the conception of self. The human beings perceive nothing simple and continuous and any idea that has no corresponding impression is considered as an unreality.
Such a theory of soul is not accepted by some realists who approach the problems of philosophy in the scientific spirit of early Buddhism. Self is defined as a generic idea standing for a collection of mental states and an accumulation of conscious contents. The view of Nagasena is perfectly logical. According to Plato, behind every individual being like chariot there is a universal lurking, there is no need to consider that the complex man has a self behind him.
If sense is considered as the measure of the universe, then experience becomes the feeling of each moment. Self is defined as an isolated momentary perception and it exists only so long as the indivisible, momentary consciousness lasts. According to William James, the pulse of the present moment is the real subject: "Consciousness may be represented as a stream. Things which are known together are known in single pulses of that stream". The real subject is not an enduring being and the survival of each subject is momentary. The subject for the time being knows and adopts its predecessor, and by so doing appropriates what its predecessor adopted. The concept of self logically becomes a transitory state of consciousness and each conscious phenomenon which is the mind is not a modification of any eternal mind stuff or the appearance of and Atman'. It is only a highly complex compound that is changing constantly and giving rise to new combinations.
Nagasena's Buddhist theory of self has been the subject of immense interest amongst the philosophers of all ages. Eminent philosophers from the West like Bertrand Russell and Kant have dealt in details with Nagasena's theory. Even today this theory is regarded as an important part of Buddhist philosophy.