Means of valid knowledge
Before you can argue about reality, you need to agree on what even counts as genuine knowing — Buddhist thinkers built a whole science of it.
Pramāṇa (Sanskrit, "means of valid knowledge," or "measure" of truth) names the instruments by which we can reliably know anything at all. Roughly between the 5th and 7th centuries CE, Buddhist thinkers — above all the philosophers Dignāga and Dharmakīrti — built this into a rigorous tradition of logic and epistemology, the study of how knowledge works. It carried on lively debate with the Hindu philosophical schools of India, which had their own theories of valid knowing; the question of what counts as real knowledge was a shared pan-Indian project, and the Buddhists made a distinctive contribution to it. (This was a tradition of logic and reasoning rather than a doctrine unique to any one branch of Buddhism, though its great architects worked within the Mahāyāna intellectual world.)
These thinkers argued that there are essentially two trustworthy means of knowledge. The first is perception (pratyakṣa): direct, bare sensory awareness of a particular, before the mind layers concepts and names onto it. The second is inference (anumāna): reasoning that moves reliably from evidence to conclusion — seeing smoke and validly concluding there is fire. Other supposed sources, such as mere testimony or scripture taken on its own authority, were not granted independent standing as separate means; they had to reduce to perception or sound inference.
This was not dry logic-chopping. By pinning down exactly what makes a cognition valid, Buddhist epistemologists could defend core teachings against rival philosophers and sharpen their own analysis of mind and reality — including subtle theories like apoha, the account of how words mean by exclusion. The pramāṇa tradition became one of the great achievements of Indian philosophy, prized later in Tibet, where its texts are still debated in monastic courtyards.