The purpose of this article is to set out the concept of conditional origin (pratitya-samutpada) in Nagarjuna’s thinking. That concept is the basis of its doctrine of vacuity, according to which everything is empty, insubstantial and devoid of its own nature, precisely because it has a dependent origin. Nagarjuna thus destroys traditional philosophical alternatives (based on exclusive concepts) by showing that both their unilateral assertion and denial are equally inconsistent. It is not, therefore, a matter of gaining access to scepticism that would refrain from any trial, nor of proposing philosophical nihilism. Rather, we are faced with the assertion of the insubstantial interdependence of all phenomena as a fundamental reality. A subtle form of reality, which lies between being and not being, in the context of a metaphysical relational and dialectic.