Tips, Pointers, and Rules to being aGreat Debator
In logic ( 邏輯 ), an argument ismade up of a set of statements. Thefirst statements are called thepremises‘. A ‘premise’ is a sentence that willhelp support your argument. The last statement is called theconclusion. The conclusion isusually the statement that you wantsomebody to accept (agree withyou), which is why youre arguing inthe first place. Heres an example of an argument: All birds have wings. (premise)A cuckoos a bird. (premise)Therefore, a cuckoo has wings.(conclusion)
In this particularargument, the premisesforce the conclusion.Anyone who believes thepremises must also believethe conclusion. This istherefore called a validargument, or it could besaid that the conclusionfollows validly from thepremises. If something is valid it istrue.
In the previous example, bothpremises are true, so the conclusionmust be true as well. By true, wemean that they are statements thataccurately reflect reality.It is possible for an argument to bevalid, yet for the premises andconclusion to be false. For example:All Americans eat hamburgers onSundays.Tony Blair is American.Therefore, Tony Blair eatshamburgers on Sundays.Both the premises and theconclusion are demonstrably false,and yet the argument is valid.Anyone who believed both premiseswould also have to believe theconclusion. This shows that validityis a feature of the form of theargument, and has nothing to dowith its content.Can we make some examples on our own?
When an argument is valid, and the premisesare true, then the conclusion must also betrue. Then the argument is called sound, orcogent, and whoever you are arguing with isforced to agree that you are right, or else toresort to violence. Ex: Mercury destroys your nervous system. Sharks have a lot of mercury in their bodies. Eating shark can be dangerous for yournervous system.
Since validity has to do withthe form of an argument, itis possible to identify validforms, and some of thesehave been studied bylogicians, and have beengiven names in Latin. Valid Argument FormNumber One - ModusPonens Modus Ponens (proposingmode) is the most commonform of valid argument. Thecuckoo argument and theTony Blair argument aboveare both examples of ModusPonens. A generalizedModus Ponens argumentlooks like this: All A are B.x is ATherefore, x is B. This is what Modus Ponens lookslike with certain kinds ofstatements, namely thoseinvolving quantifiers. (A quantifieris a word like all, some ornone.) Modus Ponens argumentscan also be constructed withconditional statements, alsocalled if/then statements: If a Rimram yells, then aDockermarker falls.A Rimram yelled.Therefore, a Dockermarker fell. We might not know anythingabout that Rimram or aboutDockermarker, but we must admitthat the argument is perfectlyvalid, and that anyone whobelieves the premises must alsobelieve the conclusion. With a partner make 3 validarguments. You have 8 minutes.
Now, take a look at a different argument: Some vertebrates are warm-blooded. Frogsare vertebrates.Therefore, frogs are warm-blooded.This argument is invalid. Both of thepremises are true, but the conclusion isfalse. In a valid argument, the conclusion isnever false when the premises are true. Thisparticular argument is invalid becauseModus Ponens does not work with thequantifier some, only with the quantifier all.
Invalid arguments are alsocalled fallacies. Let us lookat some very common formsof fallacy: Invalid Argument FormNumber One - Affirmingthe Consequent If x, then y.y.Therefore, x. Ex. If I am hungry, then mystomach hurts. My stomach hurts. Therefore, I am hungry.
This fallacy is a common logicalmistake, sometimes calledabductive reasoning (as opposed todeductive reasoning, of which ModusPonens is an example). It may seemat first glance to make sense. It isinvalid because the conclusion doesnot follow from the premises, evenif it happens to be a true statement.It is very easy to mix this form upwith the Modus Ponens form. Heresa concrete example: If I am with the one I love, then Iam happy.I am happy.Therefore, I am with the one Ilove. With your partner make as manyinvalid arguments as you can in tenminutes.
This argument doesnt work, becausethe one you love could be far away, and youcould be happy for some other reason,perhaps having to do with food, money, orcentral nervous system stimulants. Here is avery well-known example of abductivereasoning: Fire causes smoke.There is smoke.Therefore, there is fire.
As tempting as it may be toaccept this conclusion, weonly know that fire is onecause of smoke. There mayalso be other causes, so thepresence of smoke does notnecessitate that of fire. Thestatements in this argumentare not explicitly phrased asconditional statements, or asquantified statements, butthe rules of reasoning stillapply. Fire causes smokecould be rephrased as Ifthere is fire, then there issmoke.
If x, then y.Not x.Therefore,not y. This is similar to Affirmingthe Consequent, exceptthat it takes on a negativeform. Heres an example: All dogs have four legs.Francis the Talking Muleis not a dogTherefore, Francis theTalking Mule does nothave four legs. Even though both of thepremises are true, theconclusion is false,because dogs are not theonly animals that havefour legs.
Ad homimen (meaningtowards the person)arguments and argumentsbased on authority are verysimilar fallacies. Ad hominemarguments are very commonin politics, and authority-based arguments are verycommon in religion2. In an ad hominem argument,a statement is said to bewrong because the personmaking that statement isfoolish, or biased, or hasbeen wrong before. This is afallacy because even afoolish, biased, often wrongperson can make correctstatements. Mr X says that Y istrue.But Mr X also saidthat Z was true,and was provedwrong.Therefore, Y isalso untrue.
Citing authority is like apositive version of adhominem. An argumentbased on authority is onein which a statement issaid to be true, becausethe person who made thestatement is smart, orinspired, or usually right.This is a fallacy becauseeverybody can be wrong,sometimes.
Some claim thatarguments based onhuman authority arefallacious, but thatarguments based ondivine authority arenot. This claim is nota logical one, but atheological one, andtherefore beyond thescope of this entry,thank goodness.
Circular ReasoningOne type of fallacythat is verycommon withlonger, morecomplicatedarguments is calledthe circularreasoning fallacy.Circular reasoningis when theconclusion is,itself, used as oneof the premises ofthe argument. Theconclusion thenfollows quiteeasily, but nothinghas really beenproven.
The classic example of circular reasoningruns something like this: This scripture is the inspired word of God.How do you know?Because it says so right here, in thisscripture.Why should I believe what it says there?Because this scripture is the inspired word ofGod...
Here is anotherargument. Thepremises are both(arguably) true, theform seems valid, theargument isntcircular, and yet theconclusion seemsfalse! Nothing is better thaneternal bliss. A peanut butter sandwichis better than nothing. Therefore, a peanutbutter sandwich is betterthan eternal bliss.The fallacy in this argument is left as an exercise, for theResearcher to find, with the recommendation that theResearcher brush up on his or her knowledge ofparadoxes.
Perhaps youve learned something new aboutarguing from this entry, and the next timeyou get in an argument, you will put this togood use. Remember: true premises + valid argument= true conclusion. If that doesnt seem to work, it might be wiseto back up your arguing skills with a goodworking knowledge of martial arts.