In the Heart Sutra it is says that the Bodhisattva Avalokitishvara “perceived the Five Aggregates to be empty of self-nature (svabhâv-shunyâ).” This means that while ordinary people perceive and believe physical shapes (rupa), such as the first aggregate, are real—they are not. Altogether, the phenomenality of the Five Aggregates has no essence or inherent special quality. Such we might call a false self-nature which means the aggregates are illusory. About this kind of false self-nature Candrakirti says that “We do not accept that as self-nature which is brought about by, contingent on, relative to something else.”
True self-nature or svabhâva according to Candrakirti means “own being, the very nature of a thing.” Nagarjuna, in the same vein, says that “self-nature is not brought about by anything else, [it is] unproduced, [being] that which is not dependent on, not relative to any thing other than itself, non-contingent, unconditioned.” Nirvana, for example, is this kind of self-nature.
Self-nature rightly understood mans absolute reality. Phenomenal things like the Five Aggregates are not absolute—they never can be. They have relative or contingent natures (parabhâva).
Using the example of a pot made of clay, there is really no intrinsic pot-ness in the raw clay of the pot. The shape of the pot is an abstraction that is completely empty of clay, clay being, let us say, the true self-nature. When, by accident, the pot breaks, the pot is gone—but it never actually existed in the first place as something unique or with a self-nature. Only the clay remains. The pot, if we think about it, is conditioned clay being totally dependent upon the clay whereas the raw clay is independent of pot-ness. Moreover, there is no real production of a pot beyond the clay itself. There is only the fabricated pot dependent on clay. In reality, the pot is empty, like an illusion.
To find our true self-nature or true self, which is the Tathagatagarbha, we have to look beyond the conditioned illusory world which we hold to be dear and true, including the psychophysical organism. In other words, we first have to stop clinging to phenomena which are always changing (anitya) and unsatisfactory (duhkha) which have no self or self-nature. But finding such a true self or a body of self-nature, that is, svabhâvika-kaya, is not easy, especially given the fact that we are conditioned to believe illusion is real and true reality is an illusion!