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Thejointtruthtableisdefinedasfollows:
x
y
”ifxtheny”
”ifythenx”
1
Table1:
definitionofnecessaryandsufficientsymptoms
Thatistosay:
(1)Ifeventxoccurs(eventxtrue)andeventyoccurs(eventytrue)thenthiscausalstatementistrue;
(2)Ifeventxoccurs(eventxtrue)andeventydoesnotoccur(eventyfalse)thenthiscausalstatementisfalse;
(3)Ifeventxdoesnotoccur(eventxfalse)andeventyoccurs(eventytrue)thenthiscausalstatementisfalse;
(4)Ifeventxdoesnotoccur(eventxfalse)andeventydoesnotoccur(eventyfalse)thenthiscausalstatementistrue;
(5)Ifeventyoccurs(eventytrue)andeventxoccurs(eventxtrue)thenthiscausalstatementistrue;
(6)Ifeventyoccurs(eventytrue)andeventxdoesnotoccur(eventxfalse)thenthiscausalstatementisfalse;
(7)Ifeventydoesnotoccur(eventyfalse)andeventxoccurs(eventxtrue)thenthiscausalstatementisfalse;
(8)Ifeventydoesnotoccur(eventyfalse)andeventxdoesnotoccur(eventxfalse)thenthiscausalstatementistrue.
Conclusion:
thereisacausalitybetween“eventxoccurs”and“eventyoccurs”.Ifeventxoccurstheneventywilloccurandifeventyoccurstheneventxmustoccur.
Clearly,underthiscondition“eventxoccurs”isanecessaryandsufficientsymptomof“eventyoccurs”;
“eventyoccurs”isalsoanecessaryandsufficientsymptomof“eventxoccurs”.
1.2Examples
Theexamplesbelowarelistedinordertoshowthisdefinition.
Example`1.21
Causalityanalysisof“thereisaforce=x”and“thereisacounterforce=y”.
Inthisgivencausalseries,xandyaretwoevents(phenomena),
(1)whenxoccursatthekmoment,ywilloccuratthekmomenttoo,
(2)whenxdoesnotoccuratthekmoment,ywouldnotoccuratthekmomenteither;
and,(3)whenyoccursatthekmoment,xwilloccuratthekmomenttoo,(4)whenydoesnotoccuratthekmoment,xwouldnotoccuratthekmomenteither.
Thejointtruthtableisasfollows:
Table2:
Causalityanalysisofexample1.21
(1)Ifthereisaforce(eventxtrue)andthereisacounterforce(eventytrue)thenthiscausalstatementistrue;
(2)Ifthereisaforce(eventxtrue)andthereisnocounterforce(eventyfalse)thenthiscausalstatementisfalse;
(3)Ifthereisnoforce(eventxfalse)andthereisacounterforce(eventytrue)thenthiscausalstatementisfalse;
(4)Ifthereisnoforce(eventxfalse)andthereisnocounterforce(eventyfalse)thenthiscausalstatementistrue;
(5)Ifthereisacounterforce(eventytrue)andthereisaforce(eventxtrue)thenthiscausalstatementistrue;
(6)Ifthereisacounterforce(eventytrue)andthereisnoforce(eventxfalse)thenthiscausalstatementisfalse;
(7)Ifthereisnocounterforce(eventyfalse)andthereisaforce(eventxtrue)thenthiscausalstatementisfalse;
(8)Ifthereisnocounterforce(eventyfalse)andthereisnoforce(eventxfalse)thenthiscausalstatementistrue.
thereisacausalitybetween“thereisaforce”and“thereisacounterforce”.Ifthereisaforcethentherewillbeacounterforceandifthereisacounterforcethentheremustbeaforce.
Clearly,undercertaincondition“thereisaforce”isanecessaryandsufficientsymptomof“thereisacounterforce”;
“thereisacounterforce”isalsoanecessaryandsufficientsymptomof“thereisaforce”.
Example`1.22
Causalityanalysisof“thelightbulbisemittinglight=x”,and“thelightbulbisemittingheat=y”.
Table3:
Causalityanalysisofexample1.22
(1)Ifthelightbulbisemittinglight(eventxtrue)andthelightbulbisemittingheat(eventytrue)thenthiscausalstatementistrue;
(2)Ifthelightbulbisemittinglight(eventxtrue)andthelightbulbisnotemittingheat(eventyfalse)thenthiscausalstatementisfalse;
(3)Ifthelightbulbisnotemittinglight(eventxfalse)andthelightbulbisemittingheat(eventytrue)thenthiscausalstatementisfalse;
(4)Ifthelightbulbisnotemittinglight(eventxfalse)andthelightbulbisnotemittingheat(eventyfalse)thenthiscausalstatementistrue;
(5)Ifthelightbulbisemittingheat(eventytrue)andthelightbulbisemittinglight(eventxtrue)thenthiscausalstatementistrue;
(6)Ifthelightbulbisemittingheat(eventytrue)andthelightbulbisnotemittinglight(eventxfalse)thenthiscausalstatementisfalse;
(7)Ifthelightbulbisnotemittingheat(eventyfalse)andthelightbulbisemittinglight(eventxtrue)thenthiscausalstatementisfalse;
(8)Ifthelightbulbisnotemittingheat(eventyfalse)andthelightbulbisnotemittinglight(eventxfalse)thenthiscausalstatementistrue.
thereisacausalitybetween“thelightbulbisemittinglight”and“thelightbulbisemittingheat”.Ifthelightbulbisemittinglightthenthelightbulbwillbeemittingheatandifthelightbulbisemittingheatthenthelightbulbmustbeemittinglight.
Clearly,undercertaincondition“thelightbulbisemittinglight”isanecessaryandsufficientsymptomof“thelightbulbisemittingheat”;
“thelightbulbisemittingheat”isalsoanecessaryandsufficientsymptomof“thelightbulbisemittinglight”.
Example`1.23
Causalityanalysisof“heismyopic=x”,and“theparallelraysarefocusedinfrontofhisretina=y”.
Table4:
Causalityanalysisofexample1.23
(1)Ifheismyopic(eventxtrue)andtheparallelraysarefocusedinfrontofhisretina(eventytrue)thenthiscausalstatementistrue;
(2)Ifheismyopic(eventxtrue)andtheparallelraysarenotfocusedinfrontofhisretina(eventyfalse)thenthiscausalstatementisfalse;
(3)Ifheisnotmyopic(eventxfalse)andtheparallelraysarefocusedinfrontofhisretina(eventytrue)thenthiscausalstatementisfalse;
(4)Ifheisnotmyopic(eventxfalse)andtheparallelraysarenotfocusedinfrontofhisretina(eventyfalse)thenthiscausalstatementistrue;
(5)Iftheparallelraysarefocusedinfrontofhisretina(eventytrue)andheismyopic(eventxtrue)thenthiscausalstatementistrue;
(6)Iftheparallelraysarefocusedinfrontofhisretina(eventytrue)andheisnotmyopic(eventxfalse)thenthiscausalstatementisfalse;
(7)Iftheparallelraysarenotfocusedinfrontofhisretina(eventyfalse)andheismyopic(eventxtrue)thenthiscausalstatementisfalse;
(8)Iftheparallelraysarenotfocusedinfrontofhisretina(eventyfalse)andheisnotmyopic(eventxfalse)thenthiscausalstatementistrue.
thereisacausalitybetween“heismyopic”and“theparallelraysarefocusedinfrontofhisretina”.Ifheismyopicthentheparallelrayswillbefocusedinfrontofhisretinaandiftheparallelraysarefocusedinfrontofhisretinathenhemustbemyopic.
Clearly,undercertaincondition“heismyopic”isanecessaryandsufficientsymptomof“theparallelraysarefocusedinfrontofhisretina”;
“theparallelraysarefocusedinfrontofhisretina”isalsoanecessaryandsufficientsymptomof“heismyopic”.
Example`1.24
Causalityanalysisof“thebodyishere=x”,and“theshadowishere=y”
Table5:
Causalityanalysisofexample1.24
Thati