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Logical Fallacies

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Learn about the Logical (or Formal) Fallacies. View on Prezi: http://prezi.com/vpgdlbf96nf5/fallacies/

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Logical Fallacies

  1. 1. '1 University of Santo Tomas — Graduate School FALLAC Y ~An¢nunnausm bis: lmsorung mum Ins mg aweannm of math . Amuogpi. -mi: -sng, 3 dxtmvrnlgwmm -Anerlm rmlmgiian lhe vlulzllun avanymlwc laglt - mum of reasoning 5'-VNMI la! SGPNINYV . Fallacy cummmzd wllh the mum. Indecent: u mislead . n amm- nambgm - Fzllxy wmmmm whim .2 -s Ixnpfirycd uukruvvlingly ow Ihvuufiu lh: mmmm the vulzsof waving mumxur urlnuvnou INFORMAL FMMCIES .1 :44 flimwfi :2-nu. llllrq--I ». ... .i - ems Ihalanse lmm Ihe Q amtumn in the mnnounonordmoulson . .. ... v.. .. ... 3.. ..“ oM: wmsu! :d. |loma wIongassurI1'mur ni ram or from Ignoting me me munrxuiuvunvr .1 fnllazy nl Cmss Dmlm .2 Fallacy ai Too was Diwsmn .3 Fallacy M rm Nanvw umm .4 Fzllaty av Dkmmc Dvsan mm-so: moan» - Errors man anse horn me wohuon: or me mlu oi de1inn. 'inv. awn", tnrwuyani chads-uI1‘&I| Ir(alcgol| ra| I Iwpmhmzal mingms .1 mm cl into-veu Cnmevsmn 2 F. |llxyo4IrIccrl«lObv¢nlon mums mnmzollru ivluxs-as . .m. q«rmn. ... .n. ... ... ..a . .z: .nm: ..m. _-.4. . -u. ... ... ..uu. Presentation by: '§: ~jE~j; ~_, ~;~p, -,«, Ma. Marenza D. Dangla ’”'“"""""‘ Sherine Anne D. Perez Funny :1 xv-cimnru moasns Professor: Dr. Florentino T. Timbreza : ; ‘: “.. ’.? ,:’«’1;= ..‘“f7‘»‘. '"»: ‘c; ;.. ""‘? ‘:“. « ' ' I ' . - J Fi| |iKVv1SMaIe-Paul Critical Thinking Hahn: mm; Reference: Timbreza, Florentino T. { 1992). Logic: Made Simple for Filipinos. Quezon City: Phoenix Publishing House.
  2. 2. '1 University of Santo Tomas — Graduate School FALLAC Y ~Anenunnausm bis: lmsoning mum Ins mg aweannm of mu . Amiiogpi. -mi: -s-»g, & dxtmvrnlgnrmm -Anerini rmlmgiian [he maxim aianymiwi laglt - mum of Vtfiollilfl 5'-VNMI iv! SGPNINYV . Fallacy cumrvimzd wilh the mum. Indecent: u mislead . n amm- namiagm - Fzllxy uurviivitltui whim .2 -s mpima irikniwlingly oi cimgi. the Iyiuranzed the niizsof waving murrlxur urlnuviou INFORMAL FMMCIES .1 :44 flimwfi :2-nu. llllrq--I ». ... .i - Errors Ihalanse lmm Ihe Q amiumn in the connounonordmoulioii . .. ... v.. .. ... rm. .. oM: «msus: d.i-oun- wrmugassurrjnlwi ni im at horn Ignolilq the me munrxiwiuvuwi -I niiuy 11! Cross Dmsim .2 Fulhcy ai Too Wde Diwsmn .3 Fallacy M Tm Naimw umm .4 Fzilaty av Dkmmc omm mm-so: moan» - Errors man anse imm me wohuon: 01 "It nilu oi de1inn. 'invi. divrsii: n,mrwu9an. aims. -an. a Ihrulegoilral I Iwpmhmzal wllngisms .1 niiucy cl incoweu Cnmevsim 2 ruixyai-mnmomum uumu mnnizollru ruins-as . im. q«rmn. ... .n. ... ... ..i . .zr. nmi. .»-mm-.4. . -u. ... ... ..uu. Presentation by: '§: ~jE~j; ~_, ~;~p, -,«, Ma. Marenza D. Dangla ’”'“"""""‘ Sherine Anne D. Perez «mm :1 xv-cimnru xvi-ocsns Professor: Dr. Florentino T. Timbreza : ; ‘: “.. ’.? .:’«’1;= ..‘“f7‘»‘. '"»: ‘c; ;.. ""‘? ‘:“. « ' ' I ' . - J Fi| |iKVv1SMaIe-Paul Critical Thinking flnflqn: Aintval Reference: Timbreza, Florentino T. { 1992). Logic: Made Simple for Filipinos. Quezon City: Phoenix Publishing House.
  3. 3. FALLAC Y - An erroneous or false reasoning which has the appearance of truth. — An illogical, misleading, & deceptive argument. - An error resulting from the violation of any rule of logic. - An error of reasoning. Sophism (or Sophistry) - Fallacy committed with the intention to deceive or mislead an opponent Paralogism - Fallacy committed when it is employed unknowingly or through the ignorance of the rules of reasoning.
  4. 4. - Errors that arise from the INFORMAL FALLACIES (Material Fallacies) . - . » . , , 7}’. - _ mu. wmi cm X , » ' FMLQD iii LOGK. EXAM . ‘ ; ~ ’ Becmnse HA A 9§C°. S Aim 3, I / ‘ N Vl0?QSSOR'S A Leo. «‘ V E confusion in the y ,1; V “V _ X E. .‘, «‘ Vi connotation ordenotation '; .,¢; 3 —. j L of terms used, froma g_ ‘ ' wrong assumption of facts, P or from ignoring the issue. FORMAL FALLACIES (Logical Fallacies) / /F<"« - Errors that arise from the violations of the rules of definition, division, conversion, obversion, & the categorical & hypothetical syllogisms. C’; a All cats have -Four leg; I l«'¢v‘e lliur legs. ‘Iixeq-«core, l am 5 cat. J
  5. 5. I i*' ii‘-'3 . l". 'I'-‘L-: .". .l. F/ ; LL ’. 'I.4;'. : (Material Fallacies) A ~ A .11 :4 ALQ im i ~ -7, j - ’ Because iii A pieces AW w I , rm mressons A Leo. 1: A » , i /1 , ‘ - — Errors that arise from the confusion in the connotation or denotation of terms used, from a wrong assumption of facts, " in f or from ignoring the issue.
  6. 6. FORMAL FALLACIES (Logical Fallacies) / /-<’ All Celfi l/ iavt’ -Pour legs _ ' Ila v’ {Bu la“ . Errors that arise from the mfificiw, {M32 Cat, violations of the rules of definition, division, conversion, obversion, & the categorical 8: hypothetical syllogisms.
  7. 7. V ljlljlljl FALLACIES OF DEFINITION 1. Fallacy of Too Wide Definition 2. Fallacy of Too Narrow Definition 3. Fallacy of Redundant Definition 4. Fallacy of Accidental Definition 5. Fallacy of Circular Definition 6. Fallacy of Obscure Definition 7. Fallacy of Figurative Definition Fallacy of Negative Definition lji ijlijl A A l: 3] i ljl Afl
  8. 8. FALLACIES OF DEFINITION FALLACY OF TOO WIDE DEFINITION — Violates the rule of definition which prescribes that the definiens should not be wider than the definiendum. - Arises when we decrease the connotation (essence) of the definition thus widening its denotation (definition by example). Ex. : Man is an animal. definiendum definiens In defining man as an animal, we are including in the class man more individuals that are warranted by its connotation of rationality & animality. As such, even a dog or a cow is a man.
  9. 9. FALLACIES OF DEFINITION FALLAC Y OF TOO NARROW DEFINITION — Violates the rule of definition which prescribes that the definiens must not be narrower than the definiendum. - Arises when we increase the connotation (essence) of the definition, thus narrowing the denotation (definition by example). Ex. : Man is an irritable rational animal. definiendum definiens Here, the denotation is less than what the term connotes. We are excluding from the class man all rational animals that are not irritable. mimble
  10. 10. animal dog rational irritable g. non-irritable
  11. 11. FALLACIES OF DEFINITION FALLAC Y OF REDUNDANT DEFINITION - Arises when we widen the connotation (essence) of the definition by adding an attribute or property that is not essential. Ex. : Man is a rational animal capable of learning Calculus. definiendum definiens Here, the denotation is redundant, because the capability to learn Calculus is not essential to being a man.
  12. 12. rational capable of ing Calculus pabl 7 learning Calculus
  13. 13. rational capable of learning Calculus not capable of co, . learning Calculus ») 5 6* man 9
  14. 14. FALLACIES OF DEFINITION FALLAC Y OF ACCIDENTAL DEFINITION — Arises when we widen the connotation (essence) of the definition by adding an accidental attribute. Ex. : Man is a rational being who knows how to drive a car. definiendum definiens Here, the expression ”who knows how to drive a car" makes it an accidental definition, for knowledge of driving a car does not, in any way, form a part of man's connotation nor does it follow from it. Whether or not one can drive a car, he is still a man.
  15. 15. rational knows how to am 3 3' doesn't know how to drive a A ‘ * car ITIBFI
  16. 16. rational knows how to d . We a car doesn't know E’ how to drive a 43 ‘ I‘ car man
  17. 17. FALLACIES OF DEFINITION FALLAC Y OF CIRCULAR DEFINITION — Violates the rule of definition which prescribes that the definiens should not include the definiendum or any of its synonyms. Ex. : A li_e is a falsehood. definiendum definiens Man is a human being. definiendum definiens A gentleman is a man who is gentle. definiendum definiens
  18. 18. FAI. I.AOIEs OF DEFINITION FALLAC Y OF OBSCURE DEFINITION — Violates the rule of definition which requires that the definiens should be clearer & simpler than the definiendum. - Arises when the definition contains terms or phrases more difficult to understand than the definiendum itself. Ex. : A net is a reticulated fabric decussated to regular “'“°““'e”“””‘ intervals, with interstices 8: intersections. definiens A periphrasis is a circumlocutory cycle or oratorical “ef'”'e”"””‘ sonorosity, circumscribing an atom of ideality, lost in verbal profundity. definiens
  19. 19. F. »*I. I.. ~CIF. S OF DEFINITION FALLACY OF FIGURA TIVE DEFINITION — Committed when we use excessively metaphorical or figurative language in the definiens. Ex. : Love is the silver link, the silken tie, which heart to de““"°'“d“”‘ heart, and mind to mind, in body and soul can nd_ definiens
  20. 20. FALLACIES OF DEFINITION FALLAC Y OF NEGATIVE DEFINITION — Violates the rule of definition, which demands that the definiens should not be negative. A definition is supposed to declare what a term means, not what it does not mean. Ex. : A male is one who is not female. definiendum definiens A table is a furniture that is not a chair. definiendum definiens
  21. 21. FALLACIES OF DIVISION I 1. Fallacy of Cross Division r 3. Fallacy of Too Narrow Division : ’ Fallacy of Too Wide Division '2 1 I I I. .. Fallacy of Remote Division
  22. 22. FALLACIES OF DIVISION I’-7-‘. l.I. /-". C Y OF CROSS DIVISION - Violates the golden rule of logical division: There must be only one foundation (or basis) of division at a time. Ex. : Christians Muslims Buddhists (religion) (religion) (religion) Single foundation _ / V, _ , ‘E i , i 3 * , i. /" 5 D‘ ‘ 5 1 tag I. ‘J _ " ESE Muslims Doctors Women Married (religion) (profession) (gender) (civil status) More than one (1) foundation
  23. 23. FALLACIES OF DIVISION FALLAC Y OF TOO WIDE DIVISION — Occurs when the denotation (definition by example) of the subclasses into which a term is divided exceeds the denotation of the term. Ex. : I» ‘I " Black BTOWD Yellow White Red Blue Green lAl"Ca”'°’l lMalaY5) (Asians) (Europeans) (Americans)
  24. 24. FALLACIES OF DIVISION FALLAC Y OF TOO NARROW DIVISION — Arises when the denotation of the subclasses is less than the denotation of the term. — A violation of the rule of division, which prescribes that a good division must be exhaustive or complete. Ex_; Triangle 5% A How about Equilateral isosceles me? O O : : Scalene
  25. 25. FALLACIES OF DIVISION FALLAC Y OF REMOTE DIVISION — Occurs when a class is divided not into its proximate or immediate subclasses, but into its remote subconcepts. The successive steps of logical division should proceed by graduate stages. Ex. : Organisms Man Animals Plants Filipinos Americans
  26. 26. FALLACIES OF EDUCTION Fallacy of Incorrect Conversion , Fallacy of Incorrect Obversion
  27. 27. T M FALLACIES OF EDUCTION i'-'/ ?‘. l.l. .'= "'. C Y OF Iii. ’ C ORR. -': ' C T C Oi‘! . /E RSI ON — Arises when a term is undistributed (particular) in the convertend (original proposition), then distributed (universal) in the converse (inferred proposition). Su Pp Ex. : A All Tagalogs are Filipinos. (Convertend) S P A All Filiplinos are Tagaljogs. (Converse) when converse should be: Sp Pp I Some Filipinos are Tagalogs.
  28. 28. T M FALLACIES OF EDUCTION I"-i"". .l. .I. /RC. Y OF INC ORR. -': 'C T OBV. -‘: 'RSIOi’ - Arises when, in changing the obvertend (original proposition) from affirmative to negative or from negative to affirmative, the meaning of the original proposition is changed. Ex. : A All Filipinos areAsians. (Obvertend) E No Filipinos are Asians. (Obverse) when obverse should be: E No Filipinos are E-Asians.
  29. 29. , I I FALLACIES IN CATEGORICAL SYLLOGISMS ~g, i1. Fallacy of 4 Terms (Ouaternia Terminorem) I2. Fallacy of Ambiguous Middle = iI3. Fallacy of Undistributed Middle )4. Fallacy of Negative Premises I I 4 g 5. Fallacy of Particular Premises I : ,_. )6. Fallacy of Illicit Minor ~ I I I I : - 7. Fallacy of Illicit Major
  30. 30. ‘ M FALLACIES IN CATEGORICAL SYLLOGISMS i‘-'/ :‘. l.l. .'~‘. C Y OF FOUR (1:7) T. I:'RI'viS (Ouarternio Terminorem) — Occurs if there are actually four (4) terms in the syllogism, and there is no middle (M) term that serves as the medium of comparison between the minor (S) and major (P) terms. 1 2 Ex. : All Filipinos are Orientals. 3 4 All Bulakenos are Tagalogs. Therefore, all Bulakenos are Orientals.
  31. 31. FALLACIES IN CATEGORICAL SYLLOGISMS I’-'/5'. .I. .l. /-". C Y OF / »‘. I3’iBI G U O US I'= 'iIDDl. .-': ' - Occurs when the middle term (M) is ambiguous (i. e., has two shades of meaning). Ex. : Whatever is fair is beautiful. beauty To kill an enemy in war is fair. justice Therefore, to kill an enemy in war is beautiful.
  32. 32. T M FALLACIES IN CATEGORICAL SYLLOGISMS FA! .I. /-"‘. C Y OF Ui'DISTRIBUT. ~'. :'D MIDDL. -': ' — Violates the syllogistic rule, which prescribes that the middle term (M) must be used at least once as universal in any of the premises. Sp Pp Ex. : I Some Filipinos are physicians. (M) Su Pp A All Tagalogs are Filipinos. (M) Therefore, some Tagalogs are physicians.
  33. 33. FALLACIES IN CATEGORICAL SYLLOGISMS FAL. I./ -". C Y OF i_'. -EG/5‘. TIVE PR. -': 'I'ViISi': 'S - Occurs when we draw a conclusion from two (2) negative premises. Ex. : E No Filipinos are Australians. (Universal Negative) E No Filipinos are Russians. (Universal Negative) Therefore, no Russians are Australians.
  34. 34. FALLACIES IN CATEGORICAL SYLLOGISMS FALL/5: CY OF PARTICULAR PREIVIISI. -"S — Occurs when we draw a conclusion from two (2) particular premises. Ex. : I Some Filipinos are Cebuanos. (Particular Affirmative) I Some Visayans are Cebuanos. (Particular Affirmative) Therefore, some Visayans are Filipinos.
  35. 35. FALLACIES IN CATEGORICAL SYLLOGISMS FALLAC Y OF ILLICIT MINOR — Occurs when the minor term (S) becomes universal (distributed) in the conclusion, while it is only particular (undistributed) in the minor premise. Su . . Pp . Ex. : A All plants are living organisms. (Majorpremise) (M) (P) 5U . Pp. . . A All plants are insentient. (Minor Premise) (M) (S) . . u . . . Pp . A Therefore, all insentient beings are living organisms. 4: 53%. : ea»
  36. 36. FALLACIES IN CATEGORICAL SYLLOGISMS . '-'/ I-. l. .l. /5.C Y OF ILLICIT M)’-I-.10."? — Occurs when the major term (P) becomes universal (distributed) in the conclusion, whereas it is only particular (undistributed) in the major premise. . .5.U . Pp Ex. : A Filipinos are heroic people. (Majorpremise) (M) (P) 5U. .. Pii . . E Malaysians are not Filipinos. (Minor premise) (S) (M) Su Pu E Therefore, Malaysians are not heroic people. ‘ T T in Q
  37. 37. FALLACIES OF HYPOTHETICAL SYLLOGISMS : :.I1. Fallacy of Rejecting the Antecedent , I: :eI2. Fallacy of Accepting the Consequent I: :: I3. Fallacy of Sublate—Posit (Tollendo Ponens)
  38. 38. FALLACIES IN HYPOTHETICAL SYLLOGISMS I-'/5.1.1.. ’-‘. CY OF RE]. -': ' C TING TI-. '.-': ' / I-. i. ' TEC . -.'. -‘D. -'; 'ix' T - Committed when the minor premise of a conditional syllogism rejects the antecedent. Ex. : If Juan marries Patricia, she will be happy. (Major premise) antecedent consequent Ixejects But Juan will not marry Patricia. (Minor premise) . / .3 é Therefore, Patricia will not be happy. “I _: §_ 2; W s ‘/ I1." . _‘y D 55%
  39. 39. FAI. I.AOIES IN HYPOTHETICAL SVIIOGISIVIS FALLACY OFACCEPTING THE CONSEOUENT — Committed when consequent is accepted in the minor premise. (Major premise) Ex. : If your boyfriend is sincere, then he will marry you. antecedent consequent But your boyfrien will marry you. (Minor premise) Therefore, he is sincere.
  40. 40. FALLACIES IN HYPOTHETICAL SYLLOGISMS FALL/5-. C Y OF S UBLA TE-POSI T ( Tollendo Ponens) - Committed when the minor premise in a conjunctive syllogism sublates (rejects) one conjunct, and the conclusion posits (accepts) the other. Example: (Major premise) An individual can't be in Cubao and in Quiapo at the same time. my flu, Since I am not in Cubao, I must, therefore, be in Ouiapo. (Minor premise) (Conclusion) - Committed when the minor premise whose major premise is an incomplete disjunction, sublates (rejects) one disjunct and the conclusion posits (accepts) the other. Example: (Major premise) Today is either Monday or Sunday. I s But it is not onday. Therefore, it is Sunday. (Minor premise) (Conclusion)
  41. 41. Ilogism sublates (rejects) one cc nclusion posits (accepts) the otl Example: (Major premise) An individual can't be in Cubao and in Ouiapo at the same time. W fipts Since I am not in Cubao, I must, therefore, be in Ouiapo. (Minor premise) (Conclusion) nmitted when the minor prem mise is an incomplete disjuncti
  42. 42. FALLACIES IN HYPOTHETICAL SYLLOGISMS FALL/5-. C Y OF S UBLA TE-POSI T ( Tollendo Ponens) - Committed when the minor premise in a conjunctive syllogism sublates (rejects) one conjunct, and the conclusion posits (accepts) the other. Example: (Major premise) An individual can't be in Cubao and in Quiapo at the same time. my flu, Since I am not in Cubao, I must, therefore, be in Ouiapo. (Minor premise) (Conclusion) - Committed when the minor premise whose major premise is an incomplete disjunction, sublates (rejects) one disjunct and the conclusion posits (accepts) the other. Example: (Major premise) Today is either Monday or Sunday. I s But it is not onday. Therefore, it is Sunday. (Minor premise) (Conclusion)
  43. 43. edisjunct and the coni Example: (Major premise) Today is either Monday or Sunday. re/ V flu But it is not Monday. Therefore, it is Sunday. (Minor premise) (Conclusion)
  44. 44. '1 University of Santo Tomas — Graduate School FALLAC Y ~Ane1mnnc1usm Izise lnmriing mum ins mg zweannm of 111.111 . An1iiogpi. mi= -sng, & dxemvrnlgnrmm -Anerioi rmlmglian the violation 1-Ianyiulcol laglt - Arturo! of mean; 5'-VNMI Iv! SGPIWIYI . Fallacy cumrvilnzd wilh the intention Indecent: 1. mislead .1. amm- Ihnabgbm - Fzilxy mmm «hm .2 -s mpima irikniwlingly oi mmgi. the Iyiaranzed the nilesof . m.1a. .g Fuurrlxar orlnuviou INFORMAL FALLACIES .1 :44 nuswn :2-nu. 1.. ... .) ». ... .I - Enurs Ihalanse Imm Ihe Q amtuw. in the connounonordenoulioii . VIHVM . ... . . ... ... oM: «1v1s1md. i1o1na wrmugassurrjnlwi ni ram 01 imi Ignolilq the me munrxiwiuvuwi .1 fallacy 1.1 Cross Dmim .2 raiixy ai Too Wde Diwsmn .2 Fallacy M Tm Naimw umm .4 Fallacy of wmum maxi mm-so: moan» - Errors man anse imi me wolluons of 1). : nilu oi de1inn. 'invi. divrsii: r1,mrwu9an. ulna: -nu-1, a Iilrulqoilral I iwpmhmzal syllngislns .1 niiiucy oi («m1 Cnmevsion 2 F. |ilxyaIIn<arI«lObv¢nion uumu . ..m1m-cu svuixs-as .1m. qaum11a. ... ..11.. ... ... .i . .zr. nm1.. .»-mm-.4. . -u. ... .1.. .uu. Presentation by: '§: ~jE, ~j; ~_, ~,; ~_~, ,-, «, Ma. Marenza D. Dangla ’”'“"""""‘ Sherine Anne D. Perez «mm :1 mmmn. xmocsns Professor: Dr. Florentino T. Timbreza : ; ‘: “.. ’.? .:’«’1;. ..‘“f7‘»‘. '". :‘c; ;.. ""‘? ‘:“. . ' ' I ' . - J Fi| iiKVv1SMaIe-Paul Critical Thinking flnflqn: Aintval Reference: Timbreza, Florentino T. { 1992). Logic: Made Simple for Filipinos. Quezon City: Phoenix Publishing House.

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