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HUM Chapter Notes for final exam.docx

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Ted Petit

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Chapter Notes Final ExamOn April 26 2012 Part 3 Arguments Chapter 8 Inductive Reasoning 270324Deductive argument is intended to provide logically conclusive support for its conclusion such an argument is valid or invalid sound or unsound Inductive argument is intended to supply only probable support for its conclusion strong if it succeeds and weak if it failsThe conclusion of an inductively strong argument is simply more likely to be true than not If the arguments premises are true it is said to be cogent Unlike valid deductive arguments an inductively strong argument cannot guarantee that the conclusion is true but it can render the conclusion probably true even highly likely to be trueInductive arguments cannot give us certainly but they can give us high levels of probability Inductive reasoning gives us most of what we know about the empirical workings of the world allowing us in science to soar reliably from what we know to what we dontInductive arguments come in several forms 4 including enumerative analogical and casual Also inference to the best explanation ch9 1 Enumerative Induction Sometimes an inductive argument reasons from premises about a group or class of things to a conclusion about a single member of the groupEnumerative InductionAn inductive argument pattern in which we reason from premises about individual members of a group to conclusions about the group as a wholeFar more inductive arguments do the enumerative induction pattern In such cases we begin with observations about some members of the group and end with a generalization about all of them Its a way of reasoning that we all find both natural and usefulEnumerative induction has this form X per cent of the observed members of group A have property P Therefore X per cent of all members of group A probably have property PEnumerative induction comes with some useful terminologyTarget population target group In enumerative induction the whole collection of individuals under studySample members sample In enumerative induction the observed members of the target groupRelevant property property in question In enumerative induction a property or characteristic that is of interest in the target groupRemember that an inductive argument cannot only be strong or weak but it can also vary in its strength in the degree of support that the premises give to the conclusion So the strength of the argument depends on the premises as well as on how much is claimed in the conclusionEnumerative inductive arguments can fail to be strong in the two following major ways Its sample can be 1 too small or 2 not representative Its possible for an enumerative induction to be perfectly strong but to have false premises in which case the argument isnt cogent The data or evidence stated in the premises could have been misinterpreted fabricated or misstatedSample Size Just about everyone at one time or another probably makes this kind of mistake which is known as hasty generalizationHasty generalization The fallacy of drawing a conclusion about a target group on the basis of too small a samplePeople regularly make this mistake when dealing with all sorts of enumerative inductive evidence political polls consumer opinion and surveys scientific and medical studies etcIn general the larger the sample the more likely it is to reliably reflect the nature of the larger group In many cases our common sense tells us when a sample is or is not large enough to draw reliable conclusions about a particular target group A rule of thumb is the more homogenous a target group is in relevant to the property in question the smaller the sample can be The less homogenous the larger the sample should beIn social psychological and cultural properties people are too diverse to judge a large target group by just a few of its members In biological properties however Homo sapiens are relatively uniform We need to survey only one normal member of the species to find out if humans have earsRepresentativenessIn addition to being the proper size a sample must be a representative sample If it doesnt properly represent the target group its a biased sampleRepresentative sample In enumerative induction a sample that resembles the target group in all relevant waysBiased sample A sample that does not properly represent the target groupAn enumerative inductive argument is strong only if the sample is representative of the wholeMany arguments using unrepresentative samples are ludicrous ridiculous others are more subtle thoughtfulTo be truly representative the sample must be like the target group by 1 having all the same relevant characteristics and 2 having them in the same proportions that the target group does The relevant characteristic is features that could influence the property in questionWe are often guilty of biased sampling in everyday situations One way this happens is through a phenomenon called selective attention we notice certain things and ignore others usually without even being aware that were doing it We may ignore facts that contradict our beliefs and search out facts that support themOpinion Polls Enumerative inductions reach a high level of sophistication in the form of opinion polls conducted by professional polling organizations Opinion polls are used to arrive at generalizations about everything Opinion polls are still essentially inductive arguments and must be judged accordinglySo as inductive arguments opinion polls should 1 be strong and 2 have true premises Any opinion poll worth believing must 1 use a sample that is largely enough to represent the target population accurately in all the relevant population features and 2 generate accurate dataA poll can fail to meet this latter final requirement through dataprocessing errors botched messed up polling interviews poorly phrased questions restricted choices and order of questionsEx polling organizations such as Environics and IpsosReid regularly conduct polls in which the target group is Canadian adults more than 25 million and the representative sample consists of only 10001500 individuals How can this be By using random samplingRandom sample A sample that is selected randomly from a target group in such a way as to ensure that the sample is representative In a simple random selection every member of the target group has an equal chance of being selected for the sample
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