MỤC LỤC
Lap cac su vat da dugc tach rieng ra nhu vay dugc bieu thi bang motkhai niem Vi du: khai niem ‘hoc sinh ” biSu thi mgt lap nguai co dac diem chung la di hoc; khai niem “toi pham ” bieuthi lop cac su vat co dac diem chung - theo Bo luat hinh su cua Nuac Cong hoa Xa hoi chu nghia Viet Nam - la “hanh vi nguy hiem cho xa hoi Suae quySinh trong bp luat hinh su, do nguai cd nang luc, trach nhiem hinh su thuc hien mot each co y hoac voy. Aristote dugc coi la nguai khai sinh ra logic hoc “khong phai vi ong la ngudi dau tiSn da he thong hoa dugc cac thao tac suy luan von truac ong chi tontai riSng re, chua ro rang, ma chinh la vi ong la nguai dau tiSn da lam cho cacthao tac do trathanh doi tuvng nghien cicu, lam thanh ddi tugng nghiSn cuu chinh cac thao tac suy luan do, voi tu each la cac chinh the, chu khong chi la thanh to nay hay thanh to khac cua suy luan”5.
Ham doi twang la mot bieuthuc ngon ngu (thuong la mot ten chung) ma khi dung ket hgp vai mot hoac mot so hing doi tugng thi xac dinh. mpt hang doi tugng khac. Ham doitugng con dugc dung cap vai cac bien doi tugng. Ham doi tugng dung cap vai n bien hoac hing doi tugng thi gpi la ham n ngoi. Ta co thi coikhai niem ham doi tugng la su khai quat hoa cua khai niem ham so trong toan hoc. Vi dp: Bieu thuc “Dai hoc Qudc gia” la mot ham doi tugng. Khi ket hgp no vai hing doi tugng "Thanh pho Ho ChiMinh ”, ta dugc hing doi tugng moi la “Dai hoc Qudc gia Thanh pho Ho Chi Minh ”, con neu ket hgp n6 vai hSng ddi tugng “Ha Npi” ta lai dugc hang doi tugng moi la. “Dpi hpc QudcgiaHaNpi”. c) Vi tu (predicate). Phuong phdp dich cau (menh de) tic ngon ngic tu nhien sang ngon ngu logic vf tic. V&imenh de dan can thuc hien cac buac sau:. f Phan tich cau de xac djnh vj tu va clc hyn tu tuong ung vdi n6. Neu mot han tu dugc cau thanh tir mpt ham dbi tugng va mpt so hyn tir kh&c. thi no dirge bieu dien bing each viet ham doi tuomg tnioc, sau d6 liet ke vao trong cap ngoScdom mor dong cac hantu tirong ung, neu so nay nhieu thi dung dauphiy dS ngan each chung. Viet vi tir, liet ke cac han tu tuong ung vao trong cap ngoac don de ngay sau vi tir. Neu co nhieu han tu thi dung dau phiy de phan each chung. Ta se goi each bieuthi cau nhu the nay la each viet vi tur, hay dang vi tir cua cau. Thay the vi tu va cac han tu trong each viet vi tu bang cac ky hieu tuorag ung quy dinh trong phan heky tu cua ngon ngu logic vi tu. Vi diyCho menh ^e“Me Mai la bac si”. Truac het, can phan tich cau de xac dinh cac thanh phan ngic nghia cua no. Rd rang cau nay la. bac si” va tinh chat“bac sT'nhu nhau, nen ve sau ta se lupc Z>d“la”, ta ciing lupc bo nhu vay vffi cac vi tic khac).
Dieu nay cd nghia la o cac qua trinh tu duy khac nhau ta cd the dung tu vdi nhidu nghia khac nhau, tu tuong cd thd cd nhung gia tri chan ly khac nhau, nhung trong cung mot qua trinh suy luan thi th ngu bao gid cung dugc dung voi mgt nghia duy nhat, tu tuong phai cd cung mot ngi dung duy nhat, phai cd cfmg mgt gia trj chan ly duy nhat. Doi khi ta gap nhung cau n6i rat sau sic ma bieu hien true tiep la quy luat triet tam.Vi du, cuoi bo sach ‘Tam quoc diin nghia”, sau khi ke chuyen nha Tan thong nhit Trung Quoc, tac gia La Quan Trung da viet, dai y: Lich su cac nuac cu nhu vay, het hop thi tan, het tan roi lai hop.
Ve mat ket cau, khai niem gom hai yeu to la npi ham va ngoai dien (con goi la ngoaidien). Npi ham la tap hop tat ca cac dau hieu lam co so cho viec khai quat hoa va tach rieng ra thanh mot lap cac ddi tupng phan anh trong khai niem. Nhu vay npi ham cuakhainiem chinh la tap hop tat ca cac dau hieu cobancua doi tuong dupe phan anh trong khai niem. Vi du, noi ham cua khai niem ”con ngudi" la tap hop cac tinh chat: dong vat, biet che tao cong cu lao dongva biet su dung cong cu lao dong. Ngoai dien cua khai niem la tap hop tat ca cac doi tuong co cac ddu hieu neu trong npi ham cua khai niem. Vi du, ngoai dien cua khai niem. c) Khai niem va tic. Khai niem bao gid cung gan voi tir. The nhung tu khong phai la khai niem. That vay, cung mot tu nhu nhau nhung co the bieu thi nhung khai niem khac nhau. Nhung khai niem khac nhau cung dupe the hien bang mot tuchinh la cai ma ta van goi la nhftng each hieukhac nhau ve tu nay. Chang han, tu "Niet ban" co the dupe hieu nhu tu chi chon cue lac ma nhung ngudi die dao dupe den o, va cung co the dupe hieu nhu la mot trang thai dac biet cua linh hon, cua tarn linh. Ngupc lai, nhieu tir khac nhau lai co thi dupe hiiu nhu nhau, nghTa la bieu thi cung mot khai niem. Cacloai• khai niem•. Ngudi ta co thi chia loai khai niem theo nhung co so khac nhau. Sau day chung ta xetmot sd kieu chia loai quan trong nhlt. Can cu vao noi ham co the chia khai niem thanh khai niem cu the va khai niem truu tuong. Khai niem phan dnh cac doi tuong ton tai dpc lap goi la khai niem cu thi. Khai niem noi vi cac dac tinh, tinh chat cua cac ddi tupng - nhung thu khong tdn tai dpc lap con ban than cac ddi tupng thi dupe lang quen, la khdi niem truu tupng. b) Can cicvao dau hieu theo do khai qudt hda. Nguoi ta ggi kieu dinh nghia nay la dinh nghia Ostensio (chi ra). Day khong hin la dinh nghia, vi khong neu len y nghia cua tu va cum tu can dinh nghia. No co gioi han han ch6, nhung co vai tro to Ion, vi mot khdi lugng Ion tri thuc chung ta thu dugc hoi con be la thong qua loaidinh nghia nay. Cac quy tac dinh nghia. Quy tac l:Dinh nghia phai can doi day du. Nghia la ngoai dien cua khai niem can dinh nghia va ngoai dien khai niem dinh nghia phai nhu nhau. Ndu ngoai dien cua khai niem dugc dinh nghia hep hon ngoai dien cua khai niem dung dd dinh nghia thi dinh nghia do qua rpng, ngugc lai, ndu ngoai dien cua khai niem can dinh nghia rong hem ngoai dien cua khai niem dung dd dinh nghia thi dinh nghia do qua hep. Dd thuc hien dugc doi hoi nay, ta phai neu du cac dau hieu ban chat cua doi tugng dugc khai niem phan anh. Vi du, trong dinh nghia con nguoi cua Platon "Con ngu&i la con vat di bang hai chan va khong cd long vu" ta thay nhieu dau hieu ban chit cua con nguoi nhu biet che tao va su dung cong cu lao dong, v.v. khong dugc neu, va chinh vi vay dinh nghia nay tro nen qua rpng, chim vat long cung la nguoi theo dinh nghia nay. Quy tac 2:Khdng dupe cd vdng tron logic trong dinh nghia. Nghia la khong dugc dinh nghia Dfd thong qua Dfii, roi Dfh lai dugc dinh nghia true tiep hoac gian tiep thong qua Dfd. Vi pham quy tac nay ta gpi la dinh nghia lin quan. Quy tac 3:Dinh nghiaphai ro rang, ngan gpn. Nghia la tu dung d6 dinh nghia khong doi hoi dugc dinh nghia nua. Dinh nghiaphai dugc trinh bay ngSn gpn, chi neu vua du cac dac diem co. ban giup xac dinh doi tugng ma thoi, nhung dac diem khac, du la dac diim co ban, nhung c6 the rut ra dupe tu cac dac diem da neu thi khong cin neu nua. Tuy nhien, trong thuc te, doi khi de dat duoc nhung hieu qua nao do, ching han vi yeu cau su pham, nguoi ta vi pham mot each cd y quy tac nay. Quy tac 4:Cacddu hieu dungtrongdinh nghiaphai la cac ddu hieu ban chat. Quy tac 5:Khdngnen dinh nghia bang cac ddu hieuphu dinh. N6u dinh nghia bing each neu cac dau hieu phu dinh thi ta kho xac dinh duoc doi tuong duoc khai niem phan anh. Nhung trong mot so truong hop, vi du trong toan hoc, nhung dinh nghia nhu the lai hoan toan cho phep xac dinh doi tuong. Quy tac 6:Khdng sic dung cac tic ngic hoa my hoac nghia bong, nghia andu cua tic ngichoac cua cau de dinh nghia. Phai tuan thu quy tic nay vi yeu caudau tien va quan trong nhat cua dinh nghia khai niem la giup xac dinh npi ham va ngoai dien cua khai niem. Ndu khong tuan thu quy tic nay thi nguoi nghe, nguoi doc co the hiiu dinh nghia khac voi nguoi dua ra n6. CAC THAO TAC LOGIC DOIv6l KHAI NIEM 1. Mfr r§ng va thu h§p khai niem. a) M& rong khai niem. Thao tac logic di tu khai niem voi ngoai dien hep din khai niem voi ngoai dien rong hon, bao ham no, gpi la mo rong khai niem. Day la thao tac rat hay duoc su dung trong qua trinh nhan thuc. Ching han, sau khi nghien cuu va xdc dinh duoc mot so tinh chat nao do o mot s6 ddi tuong thupc mpt lop nhat dinh, ta tien hanh khai quat hoa cho toan bo cac ddi tupng thupc lop da neu. b) Thu hep khai nigm. Thao tac logic ditir khai niem vdi ngo^i dien rgng dSn khai niem vdi ngo^i dien hep ggi lathu hep khai ni?m. c) Cong dung cua mor rpng va thu h$p khai niem. Trong qua trinh nhan thuc ta thuong su dung cac phuong phap ddi lap vdi nhau, bd sung cho nhau nhu di tu cai chung, cai phd bi£n d€n cai rieng, cai dac thh, va di tir cai rieng, cai dac th£i den cai chung, cai phd bien. Mat hinh thuc cua cac phuong phap vira noi chinh la thu hep va mo rong khai niem Mo rong va thu hep khai niem cdn giup ta xac dinh npi ham va ngoai dien cua khai niemdugc tot hon, tao dieu kien thuan Igi cho dinhnghTa va phan chia khai niem. Phan chia khai niem. Thao tac logic xac dinh nhung khai niem hang dugc bao ham trong mot khai niem loai cho truoc goi la phan chia khai niem Ta cung co thl coi phan chia khai niem la thao tac tao ra cac khai niem moi tir mot khai niem da cho ban dau. Ngoai dien cua cac khai niem moi nay la cac phdn khac nhau cua khai niem da cho bandiu. Phan chia khai niem la mot thao tac dugc su dung rdt thuong xuyen trong qua trinh nhan thuc. Khi nghien cuu mot lop nao do gom nhiSu doi tugng ma tinh chat nghien cuu phuc tap va cd lien he chat che voi cac dac diem rieng cua cac doi tugng do thi, de cho don gian, ngudi ta tien hanh phan chia lop cacdoi tugngdang xet ra thanhnhieuphan lop roi tidnhanh nghien cuu tinh chit minh quan tarn o cac doi tugng thupc cac phan lop nhu vay. Lop cac doi tugng ban dau chinh la ngoai dien cua mot khai niem nhat dinh, cac phan lop cua no, den lugt minh, cung la ngoai dien cua nhung khai niem nao do. Thao tac nhu vay chinh la phan chia khai niem Vi du, ta cdn nghien cuu cuoc song hi?n nay cua sinh vien tai Thanh phd Ho Chi Minh. Day la mot van de kha phuc tap, lai phu thugc nhidu vao cho o hien nay cua gia dinh sinh vien, nen, de cho don gian, ta chia so sinh vien nay thanh, ching han, hai phan lop: phan lop cac sinh vien cd gia dinh hi?n dang d TP Ho Chi Minh va phan lop cac sinh vien cd gia dinh hien khong sinh song d thanh pho nay. vien hpc tai TP Ho Chi Minh cd gia dinh khong a thanh pho nay". Phan chia khdi niem giup ta tim hieu tOt han ve ngoai dien cua no. Thong thuang ta phan chiakhai nipm theo s\r bi6n ddi diu hieu: C£n cu theo mot diu hieu nhat dinh, gpi la co sd phan chia, phan ngoai dien cua khai niem ra thanh nhieu lap, tao cac khai ni?mmaivai ngoai dien la cac lop do. a) Cac loai phan chia khai niem. Phan doi: Chia ngoai dien khai niym ra lam hai phan sao cho cac khai niemtuang ung ve hai phan do mau thudn nhau. Phan ddi tuang doi de thuc hien. Ta chi can xac dinh mot tinh chat nao do ma mot so doi tupng ma khai niem ban dau phan anh co;con mot so khac khong co, tach cac ddi tuang thanh hai phan lap nhu vay roi tao cac khai niem moituang ung vai cdc phan lap do. Phan loai: Day la mot he thong phan chia khai niem long vao nhau. Khai niem ban dau dugc phan chia thanh cac khai niem con, roi cac khai niem con, den lupt chung, lai dupe dem phan chia. Qua trinh nay co the tidp tuc qua nhieu giai doan nhu vay. He thong khai niem ma ta nhan dupe cuoi cung chinh la ket qua cua phan loai. Phan loai co vai tro va gia tri rat Ian trong khoa hpc. Moi quan he giua cac khai niem trong mot he thing phan loai phan anh moi quan he tren thuc te giua cac doi tupng. Phan loai ghi nhan cac moi quan he giua cac tap hop doi tupng de xac dinh vi tri cua chung trong he thong, va qua do bietdupetinh chit cua cac doi tupng nay. Vi du ro rang nhat ve phan loai la he thong cac khai niem cua dong vat hpc, hoac phan loai cac nguyen to hoahpc. Phan loai co gia tri rat Ian trong khoa hpc. Nd giup he thong hoa cac su kien thuc nghiem, kinh nghiem va cac tri thuc rieng le da thu nhan dupe ve linh vuc nghien cuu, va nhd the dat co so cho budc phat trien tiep theo cua khoa hpc vi linh vuc nay. Chang han, bang phan loai cac nguyen to hoa hpc cua Mendeleev da he thong hoa cac tri thuc ve cac nguyen to hoa hpc trudc do, md ra mot giai doan phat trien moi cua hoa hpc - giai doan ly luan. Dong thdi, can cu vao bang phan loai nay ma Mendeleev da tien doan dupe mpt so nguyen to hoido chua biet. Can cu vao muc dp ban chat cua tinh chattheo do tidn hanhphan loyi ta c6 hai kieu phan loai khac nhau: phan loai tu nhien - tinh chit cua ddi tupng dupe su dpng lam ca sd phan loai la thupc tinh ban chit cua ddi tupng; phan loai hinh thuc - tinh chat lam ca sd phan loyi khong phai la thupc tinh ban chat cua ddi tupng. Phan loyi t\r nhien giup nghien cuu 61. dugc cdc tinh chatcua doitugng tren th\rc t6. Phan lo^i cdc nguyen td hod hgc, phan lo^i trong sinh vat hgc, .. thugc kieu ndy. Phan loai hinh thuc dugc tien hanh theo nhung dau hieu ben ngoai, no khong giup nghien cuu ban chat cua doi tugng, no giup sap xep cac doi tugng theo mot trat tu nhat dinh. Phan loai sachtheo ten sach, sap xep theo bang chu cai la phan loai thugc kieu nay. b) Cac quy tacphan chia khdi niem.
Phan doan (e) dung, nd khang dinh mot tinh trang cua cac hanh tinh trong he Mat trod, dugc tao thanhtu hai su kien: thu nhat, cac hanh tinh co quy dao hinh elfp va, thuhai, cac quy dao nay nam trong cung mot mat phAng. DS phan biet cau c6 chua phan doan va cau khong chua phan doan ta c6 thi xet xem cau do co giatri logic, nghTa la co the (ve nguyen tac) phan djnh dung hay sai hay khong. Vidu, cau Trai dat can 250 trieu nam de di het mot vdng xung quanh tarn cua giai Ngan Ha, chua dung mot phan doan, vi cau nay hoac phu hop voi thuc te, hoac khong. Con cau hoi Cd that sir cd cac the gidri song song veri the gidri cua chung ta khong?, khong khang dinh hay phu dinh bit cu diiu gi, viec xac dinh no dung hay sai la hoan toan vo nghia, vay no khong chua, khong bieu thi phan doan. Cau ‘Toi dang noi doi day” cung khong chua phan doan, vi ve nguyen tac ta khong the xac dinh no dung hay sai27. Hai cau khac nhau co thi “chua”, tuc la biiu dat, cung mot phan doan. ching han nhu hai cau: “Hing vua la chi gai, vua la giao vien cua 25 Tanoithong thuong vi thithoang, cdnhung cau dang khac cung the hien phandoan. Vi dy nhu cac cau hoi hungbi?n- cau ve hinh thuc la cau hoi, tuy nhienben trong da chua sKn cau tra loi. 26 Trong logic hinh thuc, ngoai khai niem phan doan ngucri ta con su dyng khai ni?m mynh di. Dinh nghTa neu tren kia dung voi mynh de, va chua hoan toan dung voi phdn dodn, boi yi phan doan edn ham chua n^oai nhung dye trung neu trong dinh nghTa do, mgt so dye trung khac: phan doan the hien ca quan diem cua nguoi dua ra n6, nghTa la trong phan dodn, sy khing dinh hay phu dinh tinh chat cua doi tugng ho$cmoi quan h? giua cac doitugng da dugc dua ra trong mgt cai votinh cam nhat dinhnao do. Vi bit cu con ngucri nao cungkhong the tdeh roi khdi tit cacac tinhcam cua minh, nenchi ton tyi cac phan doan ma khong ton tyi cacm?nh de trong thyc te. Nhung logic hinh thuc truu tugng hoa khia cynh quan diem tinh cam do cua phan doan trong nghien cuu, va m?nh de la ket qua cua s\r truu tugng hoa do. Ngoai ra, ngudi ta edn cd edeh hieu thurhai ve quan diem gitta m?nh di va phan doan. 6 day phdn doan dugc hieu nhu trong dinh nghTa ma ta dua ra luc diu. Phan doan dugc chua dyng trong cau, nhung khong phai la cau. Cdn mynh didugc coi la thi thing nhit, gomcAphdn dodnvd cauchua no. Xin xem them Nguyin Due Dan, Nhung nghjch lyngir nghTa, trongsdeh Cac van de logic truyen thong, quyin I, NXB DHQG TP HoChi Minh,tr. cau em” va “Hang la chi gai va Hing la giao vien cua cau em” bi6u dat cung mpt phan doan. Tit day ve sau, ngoai nhung trudmg hop c6 neu rd, khi chung toi noi den cau co nghia la chung toi muon n6i den phan doan “chua” trong cau do. Va chung toi cung se su dung song song cac tu “phan doan” va. “cau ”, Dieu nay cho phep thay the mot cau co dang khong quen thuoc bang mot cau khac tuong duong, nghia la “chua” cung phan doan voi cau ban dau. Va nhu vay viec xem xetphan doan de dang horn. Cdc loai phan dodn. Can cu vao cac tieu chi khac nhau nguoi ta co the tien hanh cac each phan chia phan doan khac nhau. Sau day, ta xet mpt so each phan chia phandoan quantrong nhat. a)Phan chia theo dp phirc hop.
Vi du, trong phan doan moi loai gam nham deu khong cd ich, chu tir loai gam nhdm va thupc tir cd ich (hay loai cd ich) deu chu dien. c) Tinh chu dien cua cac han tic trong phan doan dangI. Nhin vao cau true nay, ta thay ngay ring chu tir S khong chu dien. Dieu nay ro rang, vi phandoan noi ve mpt so S, nghia la nd chi chua thong tin ve mot so doi tupng thupc ngoai dien cua S, han nua, khong xac dinh dupe la nd noi ve nhung doi tupng nao mpt each cy the. Chinh vi vay, tirphan doan nay, neu cho biet rang a la S, va hoi luc do cd xac dinh dupe a cd dim trong so doi tupng ma phan doan noi den hay khong, ta thay rang khong the xac djnh dupe, vi khong biet chinh xac a thupc ve phan S ma phan doan noi den hay khong thupc phan do. Nghia la phan doan khong cho ta day du thong tin. de xac dinh. Tuomg t\r nhur vyy, tir phan doan nay, neu cho biet rang a la P, va hoi luc do co xac dinhduQC a co thuQC phan cua P ma phan doan noi den hay khong, ta thay rang cung khong the xac dinh duQC, vi phan doan chi noi den cac phantur cua P dong thai la phan tir cua S chu khong noi ve tat ca cac phan tur cua P, ma ta lai khong biet chinh xac a thuQC ve phan P ma phan doan noi den hay khong thuqc phan do. Vi dy: trong phan doan mot sd nha khoa hoc la nha tha, ca chu tur nha khoa hoc va thuQC tir nha tha deu khong chu dien. Nhumg phan doan dang I cung co cactrudmg hop khac, vai ngoai dien cua thuQC tula tap hop con cua ngoai dien chu tir. Trong cac phan doan nay, chu tir S, tucmg tyr nhu tnroc, khong chu dien. Nhumg thuqc tir P chu dien, vi ngoai dien cuaP luc naytriing vaiphan doi tuomg thuQC S ma phan doan noi toi, va vi vay, khi biet a la P ta biet ngay a thuQC ve cac doi tuomg ma phan doan noi tai. Vi du, trong phan doan mot so so tu nhien la so hoan toan chu tir so tic nhien khong chu dien, nhumg thuQC tir so hoan toan chu dien. d) Tinh chu dien cua cac han tictrong phan doan dang O. Cau true nay cho thay ngay rang chu tir S khong chu dien, vi phan doan noi ve mot so S, nghia la n6 chi chura thong tin vemot so doi tuomg thuQC ngoai dien cua S, horn nua, khong xac dinh duyc la n6 noi ve nhumg doi tuomg nao mot each cy the. Chinh vi vuy tir phan doan nay, neu cho biet rang a la S, thi khong the xac dinh duQC a co thuQC so doi tuqmg ma phan doan noi den hay khong, vi khong biet chinh xac a thuQC ve phan S ma phan doan noi den hay khong thuQC phan do. Nghia la phan doan khong cho ta day du thong tin de xac dinh. Nhumg thuQC tir trong phan doan nay thi chu dien. Tirphan doan nay, neu cho biet rang d6i tuomg a thuQC ngoai dien cua P thi ta co th£ tra lai duQC cau hoi lieu a co thuQCve s6 nhumg doituomg ma phan doan noi den hay khong? Vi du, trong phan doan mot sd ngicai khong thich trdi sau rieng chu tir ngicai khong chu dien, nhumg thuQC tir nguai thich trdi sau rieng chu dien. Dung cac sa do Venn de bieu thj phan doan ta co th£ xac dinh tinh chu dien cua cac hun tir tuomg doi de dang. De y ding trong sa do venn cua phan doan nguai ta guch cheo phan bi£u thi cac doi tuomg duorc phan doan noi toi. Khi do mQt hyn tir la chu dien neu hinh tron bieu thi no hoan toan khong bj gych cheo, hoyc nguQc hi, hoan toan bj g$ch cheo. Hyn tir bi g^ch cheo mQt phan, con mQt phan khong bi gach cheo thi khong chu dien. Bang sau day tong hpp cac ket qua ve tinh chu dien cua han tir trong phan doan. Chu dien dirge ghi blng dau +, khong chu dien ghi bdng dau trir khong ghi cac tnrdng hop dac biet. Nhan xet: Chu ticchu dien trongphan dodn toan the, khong chu dien trong phan dodn bo phan; thuoc tir chu dien trong phan dodnphu dinh, khong chu dien trong phdn dodn khang dinh. ' —Loai phdn dodn Han tir. Quan he giua cac phan doan thugc tinh don. Hinh vuong, tam giac logic. a) Cacphdn dodn khong so sdnh dirge la cac phan doan co chu tu hoac thugc tir khac nhau. Vi du, phan doan “khongphai Nam la sinh vien ”va ‘Nam khongphai lasinh vien ” la cac phan doan phu dinh cua phan doan “Nam la sinh vien Nhung trong logic ngudi ta chi dung mot each duy nhat de phu dinh mQt phan doan, cu the la dat phep toan phu dinh (-7) dang trudc no. Neu A la mQt phan doan thi -7 A la phan doan phu dinh cua A. Phep toan phu dinh duQc dinh nghTa b&ng bang chan ly nhu sau:. Qtiy luat va mau thuan logic. Tren kia da noi rang trong logic hai gia trj thi mQt phan doan hotic la dung, hoac la sai. Neu phan doan phu hop vdi thyc te thi nd dung, neu no khong phu hop vai thyrc te thi no sai. Noi chung, de xac dinh xem mQt phan doan cd dung hay khong ta phai doi chieu vdi thyrc tien. The nhung co mQt so truang hop khong can doi chieu true tiep vdi thuc te ta cung co the biet duQc phan doan la dung hay sai. Vi du, d mQt thai diem nhat djnh. thi phan doan tr&imua hoqc khong mica la phan doan dung. Ta biet dieu do ma khong can phai xet xem troi mua hay khong mua a thai diem d6. Nguyen nhan a day la phan doan da neu dung trong ca haitruong hop troi mua va troi khong mua o thai diem do. Ma ngoai hai truong hop do ra thi khong con truong hop nao. Nhu vay phan doan nay dung trong mpi truong hop. Nhung phan doan dung trong mpi truong hop nhu vay ta goi la phan doan hang dung, hay quy luat logic. Trai lai, d thai diem bat ky, phan doan tr&i mua va khong mua sai. No sai trong truong hop tren thuc te troi dang mua, va sai ca trong truong hop tren thuc te troi khong mua. Ma ngoai hai truong hop do ra thi khong con truong hop nao khac. Nghia la phan doan nay sai trong mpi truong hop. Nhung phan doan sai trong mpi truong hop nhu vay goi laphan doan hang sai, hay mau thuan logic. Cac khai niem quy luat va mau thuan logic vira neu co y nghia rat quan trpng. Mpt suy luan dung va chi dung khi cong thuc bieu thi no la quy luat logic, va no khong the nao dung dupe khi cong thuc bieu thi no la mpt mau thuan logic. Cac phuong phap xac dinh quy luat va mau thuan logic a) Lap bang chan ly3233.
35 Day to biic thur c6 tieu de “H3y ciing chung toi ungho moi quan he dang tien tri€n tich eye voi VietNam” do hai nghisiMy Rob Simmons Lane Evans gui toi toan the tlidnli vien ha vien trudc gicrbd phieu tai Ha vien My ve Dao luat nhan quyen Viet Nam 2003 (HR. "Minh phai biet sic dung thanh thqo may vi tinh ” theo dung nhu quan diimtruyen thong ve dien djeh, thia vi du 4(b) kho noi ring trithuc trong cac tien de khai quat horn so vdi tri thuc cd trong ket luan, vi cung deu n6i ve cung mgt doi tugmg (nudeX).
Doi chat phan doan la bien phan doan tir khing djnh thanh phu dinh va ngugc lai. Vi dp, phan doan Nguai ViptNamyeu hoa binh la phan doan khang dinh, doi chat thanh phan doan Nguai Vipt Nam khong thich chien tranh, la mpt phan doan phu djnh. De d6i chat mgt phan doan co thugc tir P nhu trong vi dp tren ta thay, trudc het phai tim khai ni?m P mau thuan vdd khai ni$m P. Cdc dang phandodn thugc tinh dondoi chat nhu sau:. Mgi nguai deu mongmuon hanh phuc. => Mpingucri deukhongmuon bathanh SeP => SaP. deu khong muon song co dan. => Ai cungmuon song cd bau co ban SiP=>SoP. Mpt so nuac the giai thu ba di theo con duangXHCN. => Mpt so nuac thupc the giai thu ba khongdi theo con duang tu ban chit nghia. Mot so thanh nien ngay naykhong thich lap gia dinh. => Mot sd thanh nien ngay nay thich songdpc than. Lay ngugc lai vi dp 11, tien dl thanh ket luan, ket luan thanh tien de ta dupe vi dp cho suy luannay. Chuy: *) Neu doi chat phan doan thu nhat ta dune phan doan thu hai nao do thi khi d6i chat phan doan thu hai nay ta duoc lai phan doan thu nhat ban dau. **) D6i chat phan doan chi nen thpc hi$n khi ta tim dupe bieu thuc ngon ngu khong chua tir "khong” bieu dat khai ni?m man thuan vdi thupc tu cua phan doan ban dau. Ching h^n, ta khong doi chat phan doan mpt so sinh vien la doan vien, vi khong tim dupe bieu thuc tieng Vipt bieu thj khai niem man thuan voi khai nipm "doan vien", ma laikhong chua tu "khong".
=> Mpt so ngu&i con nhu nhicprc, thoa hiep vai tham nhung la can bp nha nu&c. Phandoan dang S i P khong dat doi lap vj tir dirge (vi dang So P khongdao ngugc dirge).
Suy luan vai tien de phuc la suy luan dien dich, va cung nhu moi dang suy luan dien dich khac, niu suy luan vai tien de phuc hop logic va tat ca cac tien di diu dung thi kit luan cua no chic chin se dung. Nguai ta da chung minh dugc rang nhung he thong logic menh de thong dung dam bao dugc tinh chat:neu ket luan cua suy luan dung trong moi truang hgp ma cac tiende deu dung thi suy luando tuan thu cac quy tac logic cua he thing, tuc lahgp logic, la dung.
Vi du:(Suy lupn cua Omahr) Neu sdch cua cac ngai phii hpp vai Kinh Koran thisdch cua cac ngai thica nen can dot bo. Neu sdch cua cac ngai khongphu hop voi Kinh Koran thi sdch cua cac ngai co hpi nen cdn dot bo. Vay chac chan nen dot bo sdch cua cac ngai. Vi du: Neu chon thi khdi A thi co the thi vao cac truang dai hoc Jchoi kinh te. Neu chon thi khdi D cung cd the thi vao cac truang dai hoc khdi kinh te. Biet rang ban chon thikhdiA hoac D, vay ban cd the thi vao cac truangdai hoc khdikinh te. Vi du:Neu hoc cac nganh ky thuat thi ban cdn nhieu tri thuc toan hoc. Neu hoc cac nganh ngoai giao, ngoai thuang thi ban cdn biet nhieu ngoai ngu. Ban se hoc cac nganh ky thuat hoac cac nganh ngoai giao, ngoai thuang, nhu vay ban cdn nhieu tri thuc toan hoc hoac cdn biet. nhieu ngoai ngu. c) Suyluan theo cac cong thuc De Moorgan. Trong phan phan doan phuc chung ta da lam quen vai c&c cMp phdn doan, dugc bieu didn dudi dang phan dodn tuong duong, gpi la cong thuc De Moorgan:. Tu cdc congthuc nay fa cob6n dang thuc suy luan. Day la dang thuc suy luan co the tong hop duoc bang each ket hop cac suy luan theo cong thuc De Moorgan va Modus Tollens. Tuy nhien, trong thuc te nguoi ta thuong su dung chung ma khong ngo den suy luan theo quy tacDe Moorgan. Khong co C, Vay khong co A, cung khong co B). Cong thuc 4 nhan dugc bang each ap dyngmoduspone?75(dang thuc 3) vao cac cong thuc 2, 3. Cong thuc 5 nhan dugc bing each ap dungmocte ponensNao cdc cong thuc 1,3. Cong thuc 6 nhan dugc tu cac cong thuc 4, 5 bing edeh dp dyngmoetoponens. Day la ket luan canthiet. Vi du 3.Til cac tiende. Ta dung mot duang ke dpc ben trai de danh dau phan suy luan tim -7 wsinh ra tu gia dinh u. Sa di nhu vay la vi buac 8 co duac nha su dung gia dinh 7, ma gia djnh nay sai, bi bo di tu buac 9, vay cong thuc a buac 8 von phu thuoc no cung phai bi loai tru, va ve sau khong the su dung tiep. pur tien de. Trong suy luan tren day ta cung dung mgt suy luan trg giup. Ket luan cua suy luan trg giup nay cung chinh la ket luan ma ta can tim. Nhu vay, vi trong suy luan nay, de tim ket luan r vs ta gia dinh dilu ngugc lai voi no, roi tu do di den ket luan thong qua nghich ly, nen suy luan nay thuc hien theo phuong phap phan chung. Viec su dung gia dinh trong vi du 5 khac voi viec su dung gia dinh ma ta da quen thuoc trong cac vi du truoc. C5 day gia dinh dugc su dung khong phai de di den dieu ngugc lai voi no nhu trong cac vi dy da xet, ma de nit ra ket luan dang keo theo. Vay bay gio ta se chung minh dugc bang each gia dinh A diing, tuc co A. Theo truySn thuySt, nguoi dot thu vien Alecxandre la Omahr nit ra ket luan can dot sachtu cac tien de nhu sau: ‘Neu sach cua cac ngai dung voi kinh Koran thi sach cua cac ngai thica. Neu sach cua cac ngai khong dung voi kinh Koran thi sach cua cac ngai co hqi. Sach thica hoac cd hqi thi can phai dot bo Omahr c6 suy luan diing khong ?. tien de tiSnde. gia dinh ringkhong can phai dot sach. Trong suy luan nay suy luan phu trg dua lai chinhket luan ma suy luan chinh can. Nhuvay suy luan cua Omahr hop logic. Cd ba vi than That Tha, Khon Ngoan va Doi Tra trong mot. ngoi mieu no. Than That Tha luon noi that, thanDoi Tra luon noi doi, con than Khon Ngoan thi luc noi that, khi noi doi. Co ngiccri khach hoi than ben phai : Ai ngoi canh ngai ? Tra lai: Do la than Doi Tra. Sau do hoi. than ngoi giica: Ngai la ai ? Dirac cau tra lai: Ta la than Khon Ngoan. Hoi than ben trai: Ai ngoi canh ngai ? va than tra lai rang do la than That Tha. Tic do hay xdc dinh cdc vi than la than gi. Gpi cdcvi than ben trai, ngoi giica va benphai Ian heatla a, b, c. Cdc vf tic that tha, doi tra, khon ngoan dicacky hieu Ian heat la T, D, K. Cdc vi tic ba ngoi chi quan hp ,fai do noi rang ai do la gi do” la N. rang b la than Khon Ngoan. va c noib la Doi Tra thi b laDoi Tra).
Phuong phap dj bi?t rat cd ich trong nghien cuu d cac phong thf nghi^m khoa hpc, noi cd the kiem soat nghiem ngat cac yeu to tao nen mpt trubng hpp nhat djnh va nhovay dam bao dupe s\r giong nhau, ngoai tiu duy nhat mQt yeu to giua hai trudng hpp trong do hipn tupng nghien cuu cd xay ra va khong xay ra. Truoc het, nhu ta da biet, phuong phap tuong dong xac djnh di£u kipn can cuahipn tupng nghien cuu, nhung khong phai la dieu kipn du, nen khong the loai bo cac truong hop trong do cd dieu kipn can nhung hipn tupngnghien cuu khong xay ra, trong khi do thi phuong phap tuong dong lai khong the ap dpng cho mpt tap hop gom ca cac truong hpp hipn tupng xay ra lan cac truong hop hien tupng khong xay ra.
Trong khi do, suy luan tuong tu dua vao su gidng nhau giua doi tugng dang duoc khao sat voi doi tuong khac, thuong la doi tuong da duqc biet ro, biet rat cy the, nen de hiSu, denam bit d6i voi nhieu nguoi, va vi the dl thuyet phyc h<?. Vi du 2.Khi nguoi ta thuyet trinh cho nhungnguoi dan mpt vung bien np ve edi Ipi cua vipc nudi tom tren cat thi khong may nguoi nghe theo, macdu nguoi ta da lap luan rat chat che, tinh toan chi li tung khoan tien phai dau tuva muc Ipi nhan co dupe.
Nhung khi mpt luyt su chung minh sy vo tpi cua mpt bj cao; khi mpt nha kinh te chung minh sy dung dan, tinh hipu qua cua mpt ke hoach kinh doanh; khi mpt nha xa hpi hpc, bing cac con so thong ke cua minh, chung minh sy ton tai cuampt xu huong phat trien nhat dinh cua xa hpi; khi mpt nha tarn lyhpc, thong qua cac thi nghipm cua minh, chung minh sy ton tai cua mpt kha nang tu duy nao do o khi dpt,. Ngu&i tic do va ngu&i nd Ip, quy tpc va binh dan, chua ddt va nong nd, thpr ca cua phu&ng hpi va thpr ban, noi tom lai, nhung ke dp buc va nhung ngu&i bi dp bice, luon luon doi khang v&i nhau, da tien hanh mpt cupc dau tranh khong ngieng, luc cong khai, luc ngdm ngam, mpt cupc ddu tranh bao gi& ciing ket thuc hoac bang mptcupc cai tao each mang toan bp xa hpi, hoac bang su dipt vong cua hai giai cap ddu tranh vai nhau.
Neu phep chung minh mpt mpnh de trong toan hpc hoac logic hpc dam bao chic chin mpnh de do dung, khong the phan bac dupe, thi phep chung minh mpnh d8 trong cac khoa hpc xa hpi va nhan van (va nhieu khoa hpc khac) khong dam bao chic chin tinh dung dincua mpnh de. Dieu nay lien quan den quan diemve syton tai cua cac doi tugng ty tuang, trong cac nganh khoa hpc vira neu, doi tugng dirge coi la ton tai khi va chi khi c6 the chi ra phuomg phap xaydyng n6 qua mpt so buoc huu han.
Trong kieu ngvy bipn nay, dang le phai dua ra dan chung, dua ra chung cu cho lap luan cua minh, thi nha ngvy bipn Ipi d\ra vao uy tin cua ngudd khac de thay the. Giang vien noi rang, trong dieu Jdpn chit nghTa tu ban dpc quyen chu nghTaxa hpi co the thang a mpt nuac, - la khau yeu nhat cua chu nghTa tuban chic khong ddi hoiphai thang a mpt loat cac nuac tu ban chu nghTa phat trien nhat nhu trong dieu kipn cua chu nghTa tu ban tu do canh tranh.