Trairūpya


Trairūpya is a conceptual tool of Buddhist logic. The Trairūpya, ‘three conditions’, is often accredited to Dignaga though is now understood to have originated with his teacher Vasubandhu in the Vāda-vidhi'', post-reconstruction of this work by Frauwallner.
Trairūpya is a logical argument that contains three constituents which a logical ‘sign’ or ‘mark’ must fulfill to be 'valid source of knowledge' :
  1. It should be present in the case or object under consideration, the ‘subject-locus'
  2. It should be present in a ‘similar case’ or a homologue
  3. It should not be present in any ‘dissimilar case’ or heterologue
When a ‘sign’ or ‘mark’ is identified, there are three possibilities: the sign may be present in all, some, or none of the sapakṣas. Likewise, the sign may be present in all, some or none of the vipakṣas. To identify a sign, we have to assume that it is present in the pakṣa, however; that is the first condition is already satisfied. Combining these, Dignaga constructed his ‘Wheel of Reason’.