ToK - Reason 1. Reason (noun) a basis or cause, as for some belief, action, fact, event, etc 2. Reason (verb) - to think or argue in a logical manner; - to form conclusions, judgments, or inferences from facts or premises

ToK - Reason “He that will not reason is a bigot; he that cannot reason is a fool; and he that dares not reason is a slave” William Drummond

ToK - Reason The curious incident of the dog in the night.... The path is wet in the morning.... You left your mobile phone either on your desk or in your coat pocket...

ToK - Reason Deductive reasoning Inductive reasoning Informal reasoning

ToK - Reason Deductive reasoning From general to particular All humans are mortal Socrates is human Therefore Socrates is mortal Two premises and a conclusion Three terms – each occurring twice Quantifiers (This is formally called a Syllogism)

ToK - Reason 1. Argument (noun) - an oral disagreement; verbal opposition; contention; altercation: a violent argument 2. Argument (noun) - a process of reasoning; series of reasons: I couldn't follow his argument.

ToK - Reason Truth and Validity Truth: concerned with what is the case Validity: only concerned with whether conclusions follow from premises You should not say that an argument is true or false, but that it is valid or invalid

ToK - Reason Inductive reasoning From the particular to the general (the observed to the unobserved) I have never heard of a human being who didn’t die... then we generalise to... All human beings are mortal IR allows us to make generalisations about the world.

ToK - Reason Will the sun rise tomorrow? How do you know? How certain are you?

ToK - Reason Science uses inductive reasoning: Formulates general laws on the basis of limited observations - Metal A expands when heated Metal B expands when heated Metal C expands when heated..... a conclusion?

ToK - Reason Give examples of some hasty generalisations Why do you think that people are so quick to jump to conclusions? What is the difference between a prejudice, a generalisation and a scientific law?

ToK - Reason What distinguishes good generalisations? Number – you see one dog swimming Variety – different circumstances; old, young; Exceptions – find counter-examples Coherence – you should demand more evidence to support surprising claims than unsurprising ones Subject area – eg. generalisations tend to be more reliable in the natural sciences than in the social sciences

ToK - Reason Informal reasoning – Fallacies (Invalid patterns of reasoning) Post hoc ergo propter hoc – assume that because B follows A that A must be the cause of B Ad hominem fallacy – attack or support the person rather than the argument Circular reasoning – assume the truth of something you are supposed to be proving Special pleading – making an exception in your own case that you would not find acceptable if it came from someone else Equivocation – using language ambiguously Argument ad ignorantium – claim that something is true on the grounds that there is no evidence to disprove it False analogy – assume that because two things are similar in some ways that they must be similar in some further way False dilemma – assume that only two alternatives exist when there are in fact a wide range of options Loaded questions – a question that is biased because it contains a built-in assumption

ToK - Reason Since strict gun controls were introduced in Dodge City, the crime rate has risen. This shows that gun control does nothing to reduce crime. Jane said she trusted me, and she must be telling the truth because she wouldn’t lie to someone that she trusted. The ends justify the means. After all, if you want to make omelettes, you have to break eggs. Since the English always talk about the weather, if you meet someone who talks about the weather you can be sure they are from England. Since many great scientists have believed in God, there must be some truth in religion. We got on very well on both of our dates together. We are clearly well suited. Let’s get married! Do you want to be part of the solution or part of the problem? The average UK family has 2.4 children. The Smiths are very average people. Therefore they must have 2.4 children. Since no-one has been able to prove that we are alone in the universe, we must conclude that other life forms exist. Are all your family stupid, or is it just you? No breath of scandal has ever touched the Senator. So he must be an honest man. Just as you are more likely to take care of a car that you own than one that you rent, so a slave owner is more likely to take care of his slave than an employer is of his worker.

ToK - Reason Bad reasoning Ignorance Laziness Pride Prejudice

ToK - Reason You are a bar-person in a nightclub. The club has the following rule - Every person drinking alcohol must be over 20 years of age There are four situations: Person Drinking Beer Person Drinking Lemonade Person Aged 19 years Person Aged 21 years Which two situations should be investigated?

ToK - Reason You are presented with the following rule - Every card with a vowel on one side has an even number on the reverse side These are the cards: UG72 Which 2 cards should be turned over in order to find out if this rule is indeed the case?

ToK - Reason Justify your choices The two examples are formally identical. Why is it easier to spot the correct answers in the second example? Do your answers reflect something about human thinking in general?