Sunyata is regularly mistranslated into a claim that nothing exists, and the tradition anticipated the error and spent a great deal of effort on it. Emptiness is not a substance, not a void, and not nothingness. It is a property, and the property is a lack: things lack svabhava, own-being, inherent existence, a nature they possess independently of causes, conditions, parts and conceptual designation.
Nagarjuna, writing in the second century, established the position by argument rather than assertion. His method in the Mulamadhyamakakarika is to take each candidate for inherent existence, causation, motion, time, the self, the aggregates, the Buddha, nirvana, and to show that every available account of it as independently real collapses into contradiction. He then identifies emptiness with dependent origination, the doctrine already central to earlier Buddhism: to arise in dependence on conditions just is to lack inherent existence. That equivalence is the hinge of the whole system, because it means emptiness is not a denial of the world but a description of how the world is.
Two safeguards are built in. The first is the two truths: conventionally, things exist, function, and can be spoken about truthfully, and Nagarjuna insists that without conventional truth the ultimate cannot be taught. The second is that emptiness is itself empty. It is not a hidden absolute underlying appearances; treating it as one is the error the texts warn against most sharply, with the image of a medicine that kills if it is not itself expelled.
The earlier tradition had applied the analysis of no-self to persons. Mahayana extends it to all phenomena, including the elements into which the earlier Abhidharma analysis had resolved experience.