topics: |  philosophy | india | logic | language

Logic developed from the tradition of vAdavidyA, a discipline dealing
with the categories of debate.  Several vAda manuals, of which the
Nyayasutras of AkShapAda Gautama (c. 150 AD) is comparatively more
systematic. 

Debates, in AkShapAda's view, can be 
i. honest debate (vAda), where both sides are seeking the truth, 
ii. tricky-debate (jalpa), goal to win by fair means or foul
iii. desctructive debate (vitaNDA), defeat and demolish opponent by
     any means

Debates, e.g. of second type, between e.g. teachers from different
schools, would take place before a board called the madhyastha, often
a king or other sponsor.  In the third type, the winner may not even
have a position, but must defeat the opponent using only logical
arguments, explicitly destructive and negative. 

Apart from a theory of evidence (pramANa) and argument (tarka) needed
for the first type of debate, a nuumer of situations are listed for
concluding the debate and declaring one side as defeated
(nigraha-sthAna = defeat-situation).  Nyayasutras - 22 such situations
e.g. a) if opponent cannot understand your argument, b) is confused, c)
cannot reply within reasonable time, etc.  In addition, manuals list several
standard "false" rejoinders or jAti (24 such listed), as well as some
underhand tricks (chala), like equivocation and confusion of a
metaphor for the literal.  

METHOD:
AkShapAda defines a method of philosophical argumentation. Seven
categories  constituting the "prior" stage of a nyAya, 
starts with an initial doubt, whether p or not-p, and ends with a
decision: 1. doubt, 2. purpose, 3. example, 4. basic tenets,
5. the "basic limbs" of formal reasoning, 6. Supportive argument
(tarka), 7. Decision.  

LIMBS (or STEPS):
The limbs were the most important formulation.  Five limbs in a
structured reasoning, which are to be articulated in language: 

1. There is fire on the hill. 
2. For there is smoke 
3. (Wherever there is smoke, there is fire), as in the
   kitchen. 
4. This is such a cae (smoke on the hill).  now we get
sixteen cases.  

e.g. What is knowable is namable (as in Nyaya).
However, (according to Nyaya) everything can be named (expressed) in
language, so there is no vipakSha to this:
    This is nameable, because it is knowable. 

Here knowability is the sign, and is adequate for showing the
nameability of an entity. 

Uddyotkara captured another type of adequate reason or logical sign -
formulated in terms of a counterfactual.  
     The living body cannot be without a soul, for if it were it would
     have been without life. 
This is the generalized inference called "universal negative" -
kevalavyatirekin - The subject which has unique property B cannot be
without A, for then it would be without B, since the presence of A and
B mutually imply each other.  Since B is an unique property, there is
no sapakSha.

In this instance, since A is present uniquely in S and nowhere else,
we cannot derive the pervasion between A and B from example.