Hetucakra

Hetucakra is a Sanskrit text written by Dignaga (c 480-540 CE) on the application of his 'three modes’ (trairūpya) within the Indian logico-epistemic tradition of the Buddhadharma, sometimes referred to as Buddhist logic.

Dignaga formulated the 'three modes’ (trairūpya) which are three conditions required for a logical ‘sign’ or ‘mark’ (linga) to fulfill in order to establish the 'valid cognition' (pramana) of an 'inference' (anumana):

1. It should be present in the case or object under consideration, the ‘subject-locus’ (pakṣa)
2. It should be present in a ‘similar case’ or a homologue (sapakṣa)
3. It should not be present in any ‘dissimilar case’ or heterologue (vipakṣa)

When a ‘sign’ or ‘mark’ (linga) is identified, there are three possibilities: the sign may be present in all, some, or none of the sapakṣas. Similarly, the sign may be present in all, some or none of the vipakṣas. To identify a sign, by convention we accept the first condition as being satisfied. Combining these, Dignaga constructed his ‘Wheel of Reason’ (Hetucakra) with nine distinct possibilities, which may be tabulated as follows: (adapted from Matilal, 1998: p.9):

Hetucakra

1: + sapakṣa, + vipakṣa	2: + sapakṣa, -- vipakṣa	3: + sapakṣa, ± vipakṣa
4: -- sapakṣa, + vipakṣa	5: -- sapakṣa, -- vipakṣa	6: -- sapakṣa, ± vipakṣa
7: ± sapakṣa, + vipakṣa	8: ± sapakṣa, -- vipakṣa	9: ± sapakṣa, ± vipakṣa
Key: + = all, ± = some, -- = none

Of the nine possibilities within the chakra or 'wheel', Dignaga asserted that only two are illustrative of sound inference, that is they meet all three conditions, namely Numbers 2 and 8: either "+ sapakṣa - & vipakṣa" or "± sapakṣa & - vipakṣa" would fulfill the required conditions. Dignaga is insistent that at least one sapaksa must have the positive sign. Number 5 is not a case of sound inference as this is a pseudo-sign for although it satisfies the two conditions 1 and 3, it does not fulfill condition 2. Dignaga required all three conditions met to establish valid cognition. The second row does not satisfy condition 2 and hence none of Numbers 4, 5, and 6 are logical signs; they are pseudo-signs. Numbers 4 and 6 are called “contradictory” pseudo-signs—an improvement upon the old Nyāyasūtra definition of contradictory. The middle one, Number 5, is called “uniquely deviating” (asādhāraṇa), perhaps for the reason that this sign becomes an unique sign of the paksa itself, and is not found anywhere else. In Dignaga’s system, this sign cannot be a sign for anything else, it can only point to itself reflexively or to its own locus. Numbers 1, 3, 7, and 9 are also pseudo-signs. They are called the “deviating” signs, for in each case the sign occurs in some vipaksa or other, although each fulfills the second condition. This shows that at least in Dignaga’s own view, the second condition (when it is combined with the first) gives only a necessary condition for being an adequate sign, not a sufficient one. In other words, Dignaga intended all three conditions jointly to formulate a sufficient condition.

References

• Matilal, Bimal Krishna (author), Ganeri, Jonardon (editor) & (Tiwari, Heeraman)(1998). The Character of Logic in India. Albany, NY, USA: State University of New York Press. ISBN 0-7914-3739-6 (HC:acid free)