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RATIONALITY, ARGUMENTATION AND EMBARRASSMENT:
A study of four logical alternatives (catu.sko.ti) in Buddhist logic
By V. K. Bharadwaja

In   this   paper     I   shall   consider     several interconnected  issues  centering  around  the  four logical alternatives (catu.sko.ti) in Buddhist logic which,   it  seems  to  me,  involve    questions   of rationality,   argumentation,   and     philosophical embarrassment. It is my contention that philosophers who have  worked  in this  area  of Buddhist  logic during  the past fifty  years  or so have  not faced these  issues  squarely. In their  work, they  show either  an obsession  with   logic,[1] or a tilt  in favor  of  the  Inexpressible, [2] or  have  felt  a       certain  level  of  philosophical   embarrassment [3] while discussing them. Let me state these issues:

One: In the early Paali Buddhist  literature  we find  (a) not   only  expressions  "There  is  a next world"   and "There  is no next world"  but also  the forms "There is and is not a next world" and "There neither is nor is not a next world"[4], and (b) "The world  is   finite," "The  world  is  infinite," "The world  is both finite  and infinite," and "The world is neither  finite  nor infinite".[5] There  are two features   of  these  examples  (a)  and  (b) :  (1) Regarding  them  as  a  subject/predicate   form  of statement,  what  is  in  question  in  (a)  is  the existence   of the next world  (the subject  term) in each one of these four expressions; while in (b) the existence  of the world, the subject term, is not in question;  what is in question is whether or not the world  is  finite.  (2) In  both   (a) and  (b), four logical possibilities  have been taken into account: affirmation,   negation,   both    affirmation    and      negation,  and  neither  affirmation  nor  negation. These   four  possibilities  have  been  historically called catu.sko.ti, and philosophers have taken upon themselves the task of explaining them, the question being  as to how it is that  Buddha, the Enlightened One,  rejected  each  one  of  them.[6]  Naagaarjuna exploits  this rejection  as a form of argumentation against  his  critics  and opponents.[7] There  is a vast historical  gap between  the date of the Buddha and the date  of Naagaarjuna;  yet  when  one  reads Naagaarjuna's    works   one  is  surprised   by  the similarity   between   his  work  and  that  of  the Buddha in the formulation  of the four alternatives and their systematic rejection.[8]

 

 Two: Naagaarjuna  is said to have held no thesis or philosophic  position  of his own  on the grounds that he rejects  each  one of the the four   possible alternatives  and that he himself   says that "he has  no thesis  of his own or no position  to defend."[9] The  question, however, is that  if he has no thesis of his own to defend, then  what  is he doing? Is he engaged  in vitaa,[10] a form of debate in which one is  concerned  only  with  refuting  the  opponent's thesis   but  not  with  establishing  one's  own? An affirmative   answer   to  this   question    is  "an embarrassment  to  the  philosophers, " [11]  however "useful and effective  a philosophic   method"[12] it  may prove to be.

Three: The above two become  issues only when we think that both Buddha, the    Enlightened    One,   and    Naagaarjuna,   the Maadhyamaka  philosopher, were  concerned  with  the Inexpressible.   "'All  things  are  void'  is not  a       proposition.  It only  expresses  the  Inexpressible  with  the help of the conventional  truth.  The real language    here   would   be  silence."[13]  Or,  as Ramchandra   Pandeya  puts it: Since none of the four alternatives  have  been  asserted, the question  of their denial  does not arise   such that "if there be any reality, it cannot be expressed in terms of four  ko.tis."[14]

I will discuss these issues one by one.  My plan is  as follows: First, I will  pick  up  one  or two major   positions  on each  one of these   issues  and examine them in detail.  My strategy is to take into account the context in which these issues make their maiden appearance;  to draw important   distinctions, like the one between  different  types of questions; to indicate  the role which the Buddhists  assign to denying   each one of the four possible  alternatives in order   to reject  the  opponent's  position;  and finally to outline the conceptual  framework  within which both the Buddha and Naagaarjuna are operating. In the course  of my argument   I suggest  that  both argumentation and embarrassment presuppose a certain analysis  of the concept of rationality  which to my mind is too narrow  to go with the sense in which we say that `man is a rational animal'.

In the early  Paali  Buddhistic  literature,[15] four types  of questions   have  been differentiated. [1]There are questions  which ought  to be explained categorically  For example, to the question "Is form impermanent?" the  answer  is "Yes, it is."  To  the question  "Is  the  world  full  of  suffering?" the   answer   is  "Yes, it  is."  To  the  question  "Does  everyone  die?" the answer is "Yes, everyone  dies." These   are questions  which are clear in respect  of        both syntax   and semantics  and which therefore  are answered  categorically.   The  Buddhists  call  them pa~nha eka.msavyaakara.niiya.[16] [2] Then there are questions  which ought to be answered with a counter question. For   example, the question "Is consciousness  a person's  soul  or is consciousness one  thing  and the soul   another?" is responded  to with a counter question  "What do you take to be the soul?   "   The    Buddhists    call   them     pa~nha pa.tipucchavyaakara.niya.[17] [2] A  third  type  of question  is those  that   should  be set aside.  For example, the   question  "Will  the  Tathaagata  live after   his death or not?" is a question  which is to be   set   aside. Such    questions   are   called pa~nha.thapaniiyo.[18]  [3]  The  fourth    type   of question   is  those  which  ought  to  be  explained analytically and then answered.  For example, to the question  "Are all human beings reborn?" the answer is "Some are and some aren't." Questions   like these are called  pa~nha vibhajjavyaakara.niya.[19] In the case  of the  fourth  type, adequate  specification, clarification,  and  analysis  are  required  before these   questions  are  answered  correctly.  For  my purposes, two types  of question  are important: the first type of question to which a categorical answer is possible, and also  is generally  given;  and the third type of question, those questions which are to be  set   aside that    is,  the  eka.msa    and  the .thapaniiya  questions.  The remaining  two types of question require clarification and analysis but they are both  askable  and answerable   affirmatively  or        negatively  as the  case  may be.  The questions  of evidence whether that evidence  is analytic   or empirical  or whether  it  is of some  other   admissible  kind  of evidence are   definitely  relevant to the truth and falsity of their answers.

Consider first the .thapaniiya  kind of question. A .thapaniiya  question  is one  which   is to be  set aside.  Jayatilleke  sees  in this  type  "a  modern parallel   in  the  kind  of  questions   which  the Positivist  dismisses  as meaningless   and therefore unanswerable." [20] The   question, however, is: "What is  the  criterion    by  applying  which  a  certain question   is said to be set aside? One answer  which Buddhaghosa  gives is that a .thapaniiya  question is "a question  which  ought  not  to be explained  and which  ought to be set aside  on the ground   that it was not explained  by the  Exalted   one."[21] But as  Jayatilleke observes: "This is not very helpful, for he is virtually saying that these questions ought to be set aside because they have been set aside by the      Buddha."[22] Buddhaghosa's  position thus amounts to accepting  the authority of the Buddha, an authority which  even  the Buddha  himself  did not regard   as unchallengeable, and  this  is philosophically   very embarrassing.  We do need  a criterion  to  tell  a .thapaniiya from a .thapaniiya question.

Broadly, there  are two different   criteria  for identifying a.thapaniiya question: (1) the pragmatic criterion and (2) the logical criterion.  As regards  the pragmatic criterion Jayatilleke observes: "These questions  were  'to be set aside'  (.thapaniiya) on pragmatic   grounds   since  belief  in  any  of  the        possible  answers  was  considered  irrelevant   and otiose for our purpose."[23] Here the parable of the arrow is relevant.  The parable is designed to bring home   the  idea  that  what  is important   is giving urgent medical attention to the one who is shot with the arrow.  Questions  such as "Who shot the arrow?" are left to be answered  later, when an inquiry into the  incident  is  conducted.    In  the  context  of inquiry,  these   questions   are  both  askable  and      answerable;  but  in the  context  of giving  urgent medical aid to the victim, they are irrelevant.

The    second   is  the  logical   criterion.    A .thapaniiya  question  is either  (a) misleading  in form, violating  the logic of meaningful  syntax and thus rendered meaningless, or (b) it is conceptually impossible   for  us  within   a  given   conceptual framework to assign' truth values, true or false, to any  answer  given  to it.  Take, for   instance, the question  whether  the Tathaagata   will exist  after death.  An answer to it is classified  as one of the   avyaakata   theses [24]  (which    we  shall   discuss presently).  From a logical Point of view, it should be  possible  to  say  that  any  one  of  the  four alternatives is true.  The possible alternatives are [1] 'Yes, it is the  case', [2] 'No, it is  not  the case', [3] 'It is both  the case  and not the case', and [4] 'It is neither  the case  nor not the case'.

But, on   the  Buddhist   view,  none  of  the  four alternatives   "fits the case"  (upeti).  To say that the Tathaagata  exists  after death does not fit the case;  that he does not exist after  death  does not fit the case;  that  he exists  and   does  not exist after  death does not fit the case;  that he neither exists  nor does not exist   after death does not fit the  case.[25]  When  each   of  the  four  possible alternatives is rejected, then within the context in which the question  is asked, one obvious conclusion is that  it is not possible   to answer  the question "Does the Tathaagata exist  after  death?  "  This  possibility   is  not empirical;   and  one  is  led  to  surmise  that  it involves  logical  and  conceptual   confusions for instance, having  a good  syntax  grammatically   but semantically  having  a result that is a meaningless sentence  like "The Taj Mahal is kind to people  who visit  it"  or an unaskable   question  like  "Is the father   the  female  parent?  "  The  question,  for example, "Where  does  the flame  of a candle  go to when  it is blown  out?"[26] is one which  does  not admit a meaningful  answer because   it is based on a conceptual   confusion   of  two  distinct    logical concepts.  (It is interesting to observe that in the early  Paali  Buddhistic  texts  an exactly  similar example  is given.  Compare  "This  fire in front of you, which  has gone out, in which direction  has it  gone?")[27] The  question   thrives  on the  mistaken syntactical  similarity  with another question  like "Where  do  I  go  when  I fall  sick?"  The  second question is perfectly meanirigful while the first is incomprehensible.  The second  admits of a perfectly meaningful answer while the first does not.

There   is  another  type  of question  which   is regarded  as  "inappropriate"   (na  kalla)  and [28] which, like  the .thapaniiya   questions, is also  set        aside   on  the  grounds    that   it  is  "literally meaningless."[29] For  example, "What  is decay  and death  and of whom is this decay  and death?"[30] is an  inappropriate  question;    it  is  a  misleading question   to  ask  "Who   feeds    on  the  food  of consciousness?" Both are examples  of inappropriate, improper  questions  (na  kalla  pa~nha).[31]

I said earlier that questions of the first type, namely, the questions  which  ought  to be explained categorically, raise  a special  problem  about  the logical  status of their answers.  To a question  of this type like "Is the world full of suffering?" the categorical  answer  is "Yes, the world  is full  of        suffering."  What  is the  logical   status  of  this answer? Regarded  as an empirical   statement  or  an unrestricted empirical generalization it is patently false.   But  for Buddha, the Enlightened  One, it is true with absolute certainty. And we shall see later that  his  answer  to this  question   is one  of the      fundamental constituents  or presuppositions   of the Buddhist  conceptual  framework.  As such, it may be said, it is either analytically true or the question of its truth or falsity within that framework simply does not arise.  The only question one can ask about it is "Why after all should we accept this statement that   the world  is full of suffering  as true?" And there is all the  difference  in the world  between saying(1) that a statement  S is true and saying (2) that  S is accepted   to be true.  (1) may  be a good reason   for (2), but it need  not be: and from  (2), (1) need  not follow.  Besides, the reasons for (1) need  not  be the  reasons  for  (2) and  conversely also.[32] The question  "Why  after  all  should  we accept  that  the  world  is full  of suffering?" is external to Buddha's conceptual framework; and it is decidable  on  grounds  of pragmatic   considerations only.[33] Such considerations may not be regarded as rational in the narrow sense of the word "rational," the sense in which giving reasons for the truth of a statement is being rational. But, all the same, they are  not irrational, either, for  they  concern  and take  into  account  the reasons  for accepting  the statement to be true. They involve a necessary reference to our aims, motives, and   purposes,  to  our  values,  commitments,  and concerns, and even to our aesthetic  considerations, like   simplicity    and   elegance.    In    Carnap's  terminology[34] such questions  are external and not internal  to  the  Buddhist  conceptual   framework. However, I disagree  with Carnap  on the point  that only because external  questions  cannot be answered within the given linguistic framework, their answers must  be  analytically  true  with  respect  to  the framework. To my mind, they need not be, and in fact they are not analytically  true.  The statement that the world  is full of suffering  is not analytically true;  rather it expresses   our commitments,[35] and  whether  these commitments   are moral, intellectual, or  philosophical  will  depend  upon  the  type  of conceptual framework within which we operate.

There   is  a distinction  between  vyaakata  and  avyaakata  questions.  In the early  Paali  Buddhist literature   we come across four questions which have been characterized  as avyaakata.   "Vyaakata"  means "analysed,  explained,  clear,  comprehensible."[36] Thus   a    vyaakata   question   is    well-analyzed, explained, clear, and  comprehensible   such  that  a meaningful   answer  to it can  be given  within  the conceptual    framework  in  which  it  occurs.    The question is both askable and answerable  within that framework.  It  is  not  a  .thapaniiya   question, a question  which is to be set aside.  Given the types of questions we have enumerated  and differentiated, all questions other than the improper ones (na kalla  pa~nha)  and  those   that    are  to  be  set  aside (.thananiiya   pa~nha)   fall  within  the  range  of vyaakata  questions.  The questions   which are to be set aside need to be differentiated  from those that are improper or misleading. An improper question (na kalla pa~nha) is to be set aside on the grounds that it is "literally meaningless."[37] I Shall call them unaskable questions. The question 'What is decay and death  and of whom is the decay  and death?'[38] and the   question    `Who   feeds   on    the   food   of consciousness? '[39]  are  improper  and  misleading questions.  They are questions  "which are suggested  by the grammar   of the language  but which  give  or imply a false or distorted  picture of the nature of reality.[40] This  feature of  na  kalla  questions shows that they form a proper  subset  of.thapaniiya questions.  But then what  is the differentia   of na kalla questions?

Both types of questions  are those which   are to be  set  aside.    Both   types   are    grammatically well-formed also.  The two may be differentiated  on the grounds that while a na kalla question is either improper or misleading, a .thapaniiya question is set aside    (a)   on    the   strength    of    pragmatic considerations   formulated   on  the  lines  of  the parable of the arrow, or (b) on logical grounds with respect  to (i) that any answer to them fails to fit the case  (upeti) and (ii) that  any answer  to them results in an avyaakata thesis. Besides, the kind of response  which they evoke would differentiate  a na kalla from a .thapaniiya question.  In the case of na kalla   questions,   "all   four   of    the   logical alternatives  may be false,"[41] but these questions are not to be treated as .thapaniiya since they have been categorically answered.The   Nikaayas distinguish  between  the  two  types  by using  the formula `maa  h'evam'  (do not [say]   so) for  all  the four alternatives  of a .thapaniiya question, while in the case of na kalla questions, "the usual negation  'no h `idam' (it is not so) is used for each of the four alternatives."[42]

We  have  said  above  that  any  answer    to  a .thapaniiya question results in an avyaakata thesis, a thesis  which  is  unanalyzed, unexplained, is not clear,   and  is  incomprehensible.    Such  a  thesis broadly   is of two types: first, that which  affirms or denies the existence  of the nominatum [43] of the      subject   term,   and   second,  that   which,  while presupposing   the existence  of the nominatum of the subject term, affirms or denies a certain  predicate of it.[44] A, example [45] of the first type is:

     (A) (1) There is a next world
            (2) There is no next world
            (3) There is and is not a next world
            (4) There neither is nor is not a next world

 

In (A) it is the existence  of the next world   which is affirmed in (1), denied in (2), both affirmed and denied  in (3), and neither   affirmed  nor denied in (4). An example[46] of the second type is:

        (B) (1) This world is finite
            (2) This world is infinite
            (3) This world is both finite and infinite
            (4) This world is neither finite nor infinite

There are other examples  of avyaakata   theses;  but the difference  between  them as in (C) below  is in terms of the subject  and the predicate   chosen in a given   context;  or, as in (E) below, the difference is  in  terms  of  the  contrary   or  contradictory predicates  affirmed  or denied  of the subject.  An  example [47] of (C) is as follows:

         (C) (1) The soul is identical with the body
               (2) `The soul is different from the body
               (3) The  soul   is  both  identical    with   and different from the body
               (4) The  soul   is  neither  identical  with  nor different from the body.

Here   in  (C),  if(1) through   (4) are  regarded  as subject-predicate  forms  of the statement, then the difference  between (B) and (C) is in the particular subject   and predicate  chosen  in a given  context.

From the logical point of view, formally there is no difference between (B) and (C).

           (D) (1) The Tathaagata exists after death
                  (2) The Tathaagata does not exist after death
                  (3) The Tathaagata  both  exists  and  does  not exist after death
                  (4) The Tathaagata  neither exists nor does not exist after death.[48]

In (D) as in (A) the existence  of the nominatum   of the subject term is affirmed  in (1), denied in (2), both  affirmed  and  denied  in  (3) ,  and  neither affirmed nor denied in (4).  An example of (E) is as follows:

             (E) (1) The soul is happy
                   (2) The soul is unhappy
                   (3) The soul is both happy and unhappy
                   (4) The soul is neither happy nor unhappy

Here in (E) the predicates affirmed or denied of the subject  in (1) through  (4) are  contrary  and  not contradictory.[49]   An   example    in   which   the predicates   are neither contrary nor contradictory [50] is as follows:

              (F) (1) The goal can be attained by knowledge
                    (2) The goal can be attained by conduct
                    (3) The goal  can be attained  by both knowledge and conduct
                    (4) The  goal can   be  attained   by  neither knowledge nor conduct.

Any    example   in   which    the   predicates    are contradictory is the same as (B) or (C) above. In my discussion, I will restrict  myself to the forms (A) and (B) only.  From the logical point of view, it is the (A) and (B) forms which are interesting  and not the others at  least  so it seem to me.   The theses (l) through  (4) in both  (A) and   (R)are  avyaakata  theses.  The questions to which they are answers are .thapaniiya  to be set aside.  In both  (A) and  (B) each   one  of  the  four  logical  alternatives   is rejected.   This  form of rejection, at the hands  of Naagaarjuna,[51] developed  into "a very useful  and effective    philosophic   method"[52]   called    the prasa.mga  form  of argumentation,[53] that  is, the argument by reductio ad absurdum.[54]

What are we to make of the rejection of each one of the four logical  alternatives? The ground  cited for the rejection  is that  none of the alternatives fits   the  case  (upeti) .    As  far  back  as  1917 Poussin[55] treated  the four  logical  alternatives (catu.sko.ti),  as  "a  four  branched  dilemma" of   Buddhist dialectic.[56] He believes that it violates the law of contradiction. He writes: "Indians do not make a clear distinction  between  facts  and ideas, between   ideas  and words;  they have never   clearly recognized the principle of contradiction.  Buddhist dialectic   has a four branched dilemma: Nirvaa.na is existence, or non-existence, or both  existence  and non-existence, or  neither    existence     nor non-existence.  We  are  helpless."[57] I wish  that Poussin had realized that the old Aristotelian three laws  of thought  are the mark of human  rationality (and on Leibniz'  reckoning,[58] even God could  not violate     them in    particular    the    law    of contradiction), and  it does  not matter  whether  a human being   is white, black, brown, yellow, or red.

For this   reason, if for  no other.  I do not  agree with  Poussin   that  Indians, if they  are  rational enough, have  violated  the law of contradiction  in     rejecting each one of the four logical alternatives. Anyway, Poussin  was puzzled about the structure  of catu.sko.ti,   and  he  found  himself  helpless    to understand  it.  But he need  not have despaired  so very much about it.

Mrs.   Rhys Davids[59] calls the rejection of the four logical  alternatives   "Laws  of Thought."  She writes: "The import of a number of terms is set out, usually in dichotomic  division but sometimes in the distinctively  Indian method of presenting the by us so called Laws of Thought  thus, Is A B & If not, isA not B? If not, is A both B and not B? If not, is A neither  B  nor  not  B  (in  other  words  is  A  a chimera)?"[60] She  regarded  the  rejection  of the second and the third alternatives as  an  assertion,  respectively,   of  the  law   of contradiction  and the law of excluded middle.[61] Mr. B.  M. Barua agrees with Mrs.Rhys Davids but makes the bold  statement  of calling  all  four  logical alternatives  the  four  laws  of thought.  He says: "These are in their application to propositions:

        1. (If A is B), A is B
        2. A cannot be both B and not B
        3. A is either B or not B
        4. A is neither B nor not B" [62]

It needs little  argument  to point out Mr.  Barua's logical  folly.  One tends to agree with Jayatilleke that the contentions   of both Mrs.  Rhys Davids  and Mr.  Barua, that the four logical  alternatives  are laws of thought, are equally fantastic.  Buddha, the Enlightened  One, was  not  interested  in asserting logical    truths  or  inconsistent    statements   in rejecting  any one or all of the four  alternatives.

Mr. Barua's construal of the rejection of the fourth alternative  as an assertion  of the  law  of double negation    is  beyond   comprehension,  as  it  does violence   to the common sense and logic that we have learnt from the cradle.[63]

P. T. Raju's interpretation[64] of the rejection of the  catu.sko.ti  alternatives   reduces  to this: Each one of the four logical  alternatives  is about the   `suunya  (void),  which  in  mathematics  means 'zero'. He writes "Zero is the quantity of which all the four alternatives are denied: it  is neither positive, nor negative."[65] To my mind, this  is an assertion  which is the least illuminating;  and it turns   out  to  be identical   with  what  was  to be analyzed,   explained,   and     made    clear,   the  analysandum.   Besides,   Raju  makes  mistakes  like conflating   the   Buddhist    notion   of  avyaakata ("unanalyzed, unexplained,     unclear,     and incomprehensible")  with   the   Jaina    notion of avaktavya[66] ("indescribable"), on  the  one  hand, and  with   the  `Sa^mkara   Vedaantic    notion   of anirvacaniiya  ("indefinable") ,  on  the  other,  a reading  which,   to  my  mind,  is  unwarranted  and misplaced. Richard Chi [67] seeks to analyze the four logical  alternatives   in terms  of the  first-order functional   calculus.    He   utilizes   the    truth functional  logic  also when and where   this adds to clarification.   This  is  an  admirably    effective approach.  He opines  that   if one keeps  apart  the different   levels of truth and the different  points of view, the so-called puzzle about the rejection of the four logical  alternatives   does  not arise.[68]

Suppose, however, that  all  four  alternatives   are denied one and the same subject at the same level of truth  and from  the same point  of view;  then  the puzzle does arise.[69] How is it possible  to negate all four logical  alternatives   simultaneously? This problem, of course.   explains de la Vallee Poussin's         helplessness: but at the same time it cries  out for a  satisfactory   solution.  Chi's  observation  that Buddha,  the   Enlightened   One,  tackled  the  four logical alternatives by "not a rejection by negation but a rejection  by silence" is noteworthy.[70] Yet, logically, catu.sko.ti  remains a puzzle;   and there must be some way to solve it.  Chi mentions one tack suggested   by  Jayatilleke [71] to   construct   a solution   utilizing  the  notions  developed  in the many valued logics of Lukasiewiez and Lobochevsky but Chi himself does not offer  a solution  to the  puzzle  on  these  lines.

Instead, utilizing L. E. J. Brouwer and A. Heyting's Intuitionistic  negation operator, he formulates the four logical alternatives as  (1) p  (2) ¡wp (3) p ^ ¡wp  (4) ¡wp ^ ¡w¡w p.

And there he stops.[72] Chi's own solution has quite an  affinity  with  Jayatilleke's  solution  of  the problem  of catu.sko.ti.  The core  of Jayatilleke's thesis    is  that  we  treat  not-P  (in  the  four alternatives)  as   the    contrary   and   not    the contradictory of P. He writes: "We maintain that the   proposition, natt.hi paro loko, should according  to its context  be treated as the contrary  and not the contradictory  of atthi paro loko despite linguistic      form.[73]  Chi  exploits   the  notion  of  contrary negation  as found  in the Intuitionistic  logic and reformulates  the four logical alternatives  so that they could   be denied  simultaneously.[74] In a way, Chi's solution  is a reformulation  of Jayatilleke's in the strictly  formal logical   terminology  of the Intuitionist  logicians.[75] The value  of this sort of solution has implications  for the methodology to be employed  in the study of Buddhist  logic.  This, however, is   an independent  topic  which  I do  not propose   to investigate  in this paper.

Let  us call  the   operator  "¡w"  Boolean  negation operation  and the operator  "~" de Morgan negation. Unlike  de  Morgan  negation, Boolean   negation  has properties such that A & ¡wA entails B, and that ¡wA & (A v B) entails B.[76]

The  idea  of Boolean  negation  originated  in  the semantical   contexts of relevant logics;  but it can be  discussed   in  the  context  of  a  four valued semantics.   The motivation for Belnap was to "devise an  effective    logic   for  computers    (mechanical question-answering  systems) to use when there  is a real risk that the data-base  from which answers   to questions    are    to     be   inferred    may     be inconsistent."[77] The four values used are:

                   T(rue)  F(alse)  B(oth) N(one)

`T' represents the case in which the person has been told about a certain sentence  S that it is true but has not been told that it is false;   'F' when he has been   told that S is false  but not told that  it is true;'N' when the person has not been told anything: and 'B' when the person has been told both that S is true  and  also  that   S  is  false."[78]  On  this interpretation  of 'T','F','N', and  'B', using  the Morgan negation operation

              (1)  ~T=F  (2)  ~F=T  (3) ~B=B  (4) ~N=N

we  can  use,  on  the  said  four  values,  Boolean negation operation ~ and get:

                        (1) ¡wT=F (2) ¡wF=T

(1) and (2) behave  the same  way as in the case  of the operation of de Morgan negation: but (3)¡wB = N, and  (4)¡wN  = B.  Here  (3)¡wB  =  N  will  mean something   like this: "If a sentence  A is marked as both  true and false, then¡wA  cannot  be marked  as true, since  in order  for  this  to be the case  it would   have to be that A is not marked  as true (but it is).  And similarly A cannot be marked  as false since  then A would   have to be not marked  as false (but   it  is).  So A must  be  marked  as None."[79]

Similarly, justification can be given  for ¡w N  = B. Belnap   and  Dunn   remark:  "In  a  nutshell,  the difference between ~ and ¡w would seem to be that ~ is a kind of 'internal' negation, whereas ¡w is a kind of 'external'  negation.  ~ A might  be  read  as 'A is false', whereas ¡wA  should be read as 'it is not the case  that  A is true'."[80] But then  how are we to understand  "not"   in a given  context? For, we have made intelligible  Boolean negation  (¡w)in terms of de  Morgan  negation  (-) .  Given  this  situation, ordinarily    the   distinction     between ¡w and  ~  collapses so   much so that ¡w is understood  in terms of ~ only and "so we have only one kind of negation after all."[81] If this is so, then even the Boolean negation¡wcannot  be employed  with   advantage  over other alternative interpretations  given in terms of de Morgan negation to solve the centuries old puzzle of catu.sko.ti.