Logic

Nyaya means logic. Represented by the writings of Gautama, Nyaya deals with how to reason about the causative substances of the universe. The proponents of Nyaya believed in obtaining knowledge through observation and critical logic — much like modern scientists. They found that certain principles which can be experienced with sensory perception are real, calling this pratyaksha (that which can be seen and experienced). They discovered ways of investigating truth and stated that truth could be proven.

While Vaisheshika speaks about the nine causative substances of the universe, Nyaya deals with the reasoning and methodology for understanding them. Nyaya also identifies three sources of non-valid knowledge: samshaya (doubt), bhrama (faulty cognition), and tarka (hypothetical argument), and four sources of valid knowledge (pramana): Pratyaksha (Perception), Anumana (Inference), Upamana (Comparison), and Shabda (Testimony).

Ayurveda accepts these four sources of valid knowledge and applies them as diagnostic tools — from direct sensory observation of a patient to inference about dosha aggravation, comparison of disease patterns, and trust in authoritative testimony including both sacred texts and modern diagnostic instruments.