Unit 9 Evaluating arguments

Learning outcomes

By the end of this unit you should:

  • have practised identifying conclusions, premises, reasoning, assumptions, formal and informal fallacies in short and medium-length texts

Critical evaluation

Activity 1 Guide

Read the following instructions on how to evaluate an argument critically.

Being critical means providing your evaluation of the conclusion of any argument, and providing evidence to justify your decision. As this course focuses on logical thinking, you should provide evidence based on logic, and use logical terminology accurately. The following list provides an indicative guide for how to evaluate arguments.

  • identify the conclusion
  • identify the premises
  • identify any assumptions
  • identify the reasoning
  • evaluate the truth of each statement
  • identify any vague or ambiguous terms
  • evaluate the strength of evidence
  • identify the presence of any formal or informal fallacies
  • name the fallacy (if any)
  • evaluate the validty of deductive arguments
  • for valid deductive arguments name the valid propositional form
  • evaluate the soundness or cogency of the conclusion
critical thinking

Evaluating short texts

Activity 2 Aliens

Critically evaluate each of the following arguments.

  1. I have never seen an alien. Therefore, there are no aliens. - Generalizing from personal experience is a form of inductive reasoning. The premise refers to the author's experience, but the conclusion refers to the universal or general case. This is an informal fallacy known as anecdotal.
  2. There are many movies and books about aliens. If there were no aliens, there would be no films. Therefore, aliens exist.
  3. If there were no aliens, there would be no UFOs. Many people have seen UFOs. Since there are UFOs, there must be aliens.
  4. I am an alien, but on earth my body becomes human and I cannot change back into my usual green colour.
  5. Aliens are the life forms that evolved on other planets. There are other planets. Therefore, there may be other lifeforms.
  6. "We come in peace". Do not be afraid.
  7. Aliens have big heads. My teacher said I had a big head. Therefore, I am an alien.

Activity 3 COVID-19

Critically evaluate each of the following arguments.

  1. Coronavirus often causes mild illness. In mild cases, the probability of dying is low. Therefore, the probably of dying from coronavirus is low. - Both premises focus on mild illnesses. Both premises are true, but the conclusion is false. The conclusion is based on these premises but is used for all cases. This conclusion generalizes from a particular case to the universal case. Inductive reasoning is used. The conclusion is uncogent, because hen coronavirus causes severe illness, the probability of dying increases. The fallacy could be called hasty generalization
  2. The number people infected with COVID-19 is rising. People get infected by close contact. Therefore, coronavirus is transmitted by close contact.
  3. I have symptoms such as pneumonia. When infected coronavirus, symptoms of pneumonia appear. Therefore, I am infected by coronavirus.
  4. Humans have a possibility of becoming infected with coronavirus. I am a human. Therefore, I have the possibility of becoming infected with coronavirus.
  5. I have ten masks to prevent coronavirus. All the masks are white. Therefore, all masks are white.
  6. Coronavirus is an infection. If some has influenza, they would have an infection. Therefore, coronavirus is related to influenza.
  7. If people get a high fever and develop pneumonia, they have COVID-19. Now, a man has a high fever and developed pneumonia. Therefore, he has COVID-19.
  8. There are many patients infected with COVID-19 in this hospital. All patients have a high fever and developed pneumonia. When people get COVID-19, they have a high fever and develop pneumonia.
  9. A man has a high fever. If people get COVID-19, they get a high fever. A man must have COVID-19.

Activity 4 Mixed bag

Critically evaluate each of the following arguments

  1. If Tony comes to class, Jim will come to class. If Jim comes to class, Tom will come to class. Therefore, if Tony comes to class, Tom will come to class.
  2. All lions are cats. No mammals are lions. Therefore, sea lions are not mammals.
  3. Yuki is a model or a dancer. Yuki is not a dancer. Therefore, Yuki is a model.
  4. Either the course is difficult or easy. The course is not difficult. Therefore, the course is easy.
  5. All students in this university study computer science. All students in this university can program in C. Thus, all computer science students can program in C.
  6. The Japanese eat little fat and suffer fewer heart attacks than the British or the Americans. On the other hand, the French eat a lot of fat and suffer fewer heart attacks than the British or the Americans. The Italians drink lots of red wine and also suffer fewer heart attacks than the British or the Americans. Therefore, speaking English that kills you.
  7. I could not follow the argument made by Professor X in his research paper, but it was listed on the university website as the most downloaded paper in the history of the university, so it must be worth reading.
  8. Professor X conducted a telephone survey one afternoon by calling houses in a local village (n=35). From his results he concluded that 100% (35) of the respondents were either retired, stay-at-home mothers or unemployed. He then generalised from this sample survey to the city and claimed that no-one in the city (which includes this village) was employed.
  9. The professor`s suggestion to implement a limit on the number of non-Japanese allowed to attend a particular course is foolish. He claims that his aim is to give both Japanese and non-Japanese equal opportunity. That is ridiculous though. Does he also want a limit of non-Japanese in the canteen? We could create a special area for Japanese and special area for non-Japanese. In fact, we could have two entrances: one for Japanese and one for non-Japanese. It would be just like South Africa during apartheid.
  10. If a professor publishes an excellent paper in a top journal, he can rest on his laurels and do nothing else. We use the phrase “rest on his laurels” to describe a man who is satisfied with his past success and does not continue to make an effort. Professor X is resting on his laurels and doing nothing else. Thus, he must have published an excellent paper in a top journal
  11. An associate professor claims that university salaries are too low. He says executives working similar hours under similar conditions receive at least 10% more in annual income. But he will benefit from his own suggestion for an increase in salaries for every member of the university faculty. That is why I recommend that we reject this.
  12. There was a fire in a laboratory. The fire damaged scientific equipment worth millions of Yen. Professor X led the internal investigation into the cause of the fire. Based on his evaluation of the evidence, he concluded that the fire was caused by spontaneous combustion in the stomach of Student X, who has not been seen since the fire; or the fire was caused by Researcher Y, who was the only person in the laboratory who smoked. Following these two lines of enquiry, the professor noted that there was no evidence of gasoline or other flammable liquids and therefore ruled out any other possibilities. Researcher Y was not available for comment, and should Student Y reappear, the spontaneous combustion theory can also be ruled out. It seems likely that Researcher Y will take the blame for this fire.

Activity 5 Paradoxes

Understand and be prepared to explain the main issue in each of these paradoxes.

  1. Loki had no money, but made a bet with a dwarf callled Brok. Instead of money, he bet his own head. He lost the bet, and Brok came to collect his winning, namely Loki's head. However, Loki said that he only bet his head and so Brok was not allowed to take any of his neck. It became impossible to decide where the head started and the neck finished. Therefore, Brok could not take his head. This paradox is known as Loki's wager.
  2. There is a large amount (heap) of grain (e.g. when a 10 kilogram bag of rice is poured onto the same place on the floor). If I remove one grain, is the heap of grain still a heap? If I continue to remove grain one at a time, at what point, is the heap no longer a heap? This is known as Sorites paradox.

Activity 6 Computer science

Critically evaluate each of the following arguments

  1. If Java language is running, then the function of C++ language is used.If the function of C++ language is used, then we can utilize C language. Therefore, If Java language is running, we can utilize C language.
  2. In a programming course students must solve problem A or problem B. Most of the students selected to solve question A, so I also chose to solve that problem.
  3. The University of Aizu students get a final grade of either A or B. If they get A grade, then they get over 80 points in final score. If they get B grade, then they get between 66 and 79 points in final score. Therefore, they over 80 points or between 66 and 79 points in final score.
  4. If Dijkstra's algorithm has some negative weight circle, then It has infinite loop. Dijkstra's algorithm which I write has no infinite loop. Therefore, It has no negative weight circle.

Listen to these evaluations [Recordings made by students will be added here].

Activity 7 President Donald Trump

Critically evaluate each of the following arguments

  1. Donald Trump had a net worth of $4.5 billion in 2016.He hosted a popular TV show called The Apprentice for 10 years. His wife is a top fashion model. Therefore, Donald Trump was a good choice for President of the United States.
  2. A key task of the president of the US is to command the army and navy. Donald Trump has a great deal of experience commanding staff in his network of companies. Therefore, Donald Trump was elected President of the United States.
  3. Citizens of the United States could vote for Hillary Clinton or Donald Trump. Hillary Clinton was not popular because of numerous scandals. Therefore, Donald Trump was elected President.
  4. Donald Trump said that Hillary Clinton is crooked. The only time Hillary does not lie is when she does not speak, and so when she speaks, she is not telling the truth. Therefore, Donald Trump should be elected President of the United States.
  5. Donald Trump stated he was smart and so avoided paying tax. Most US citizens pay tax and so they are not smart. Since most citizens are stupid, they will not understand difficult ideas and words. Hillary Clinton is very smart and uses difficult words to say her ideas clearly and exactly. Donald Trump uses simple words to say his ideas. The stupid understand simple words and so understand him. Therefore, Donald Trump should be elected President of the United States.

Listen to these evaluations [Recordings made by students will be added here].

Activity 8 Coffee

Work alone or in pairs. Read the words in the glossary before evaluating the arguments.

  • delicate (adj): easy damaged, fragile
  • robust (adj: strong and healthy
  • arabica (n): coffee or coffee beans
  • robusta (n): coffee or coffee beans, usually used in instant coffee
  • coffee cherry (n): the fruit of a coffee plant
  • ripe (adj): ready to eat

Critically evaluate the following arguments.

  1. Coffee beans are green. Tea leaves are green. Therefore, coffee beans are tea leaves
  2. There are two species of coffee plants. There is robusta and arabica. This bean is a robusta bean. Therefore, this bean is not an arabica bean.
  3. If there are ripe cherries on the coffee plant, then coffee beans are produced. There are no coffee beans. Therefore, there were no ripe cherries.
  4. If there are ripe cherries on the coffee plant, then coffee beans are produced. There are ripe cherries. Therefore, coffee beans will be produced.
  5. The average recommended total calorie intake per adult is 2000 calories. The calorific content of one cup of coffee is a maximum of 5 calories. Therefore, the recommended number of cups of coffee per day is 400.
coffee berries
tea leaves

Evaluating medium-length texts

Activity 9 Rabbits and hedgehog

Read and identify: the claim(s), i.e. the conclusion(s), the premise(s), any assumption(s), the type of reasoning used (e.g. deductive, inductive) and any flaws or fallacies.

Two rabbits and a hedgehog were sitting talking by the side of a busy road. The hedgehog was keen to see what was on the other side of the road but was frightened of attempting the journey for fear of being run over by a car. The rabbits gave him a piece of advice: ‘If there’s a vehicle coming,’ they said, ‘look it right between the headlights, curl up in a tight ball, let it pass over the top and away you go. It’s as simple as that.’ A few minutes later, the first rabbit tried to cross the road. Half-way across, he saw a car approaching. Lining himself up directly between the car’s headlights, he curled up in a ball and allowed the wheels to pass either side of him. Then he scampered to the grass verge on the other side. Shortly afterwards, the second rabbit crossed the road. He was almost at the other side when he saw the headlights of a huge lorry. Lining himself up directly between the headlights, he curled up in a ball and allowed the wheels to pass either side of him. Then he too scampered to the grass verge. Five minutes later, the hedgehog finally plucked up the courage to try and cross the road. He had only gone a few yards when he saw headlights approaching. He lined himself up directly between the headlights, curled up in a ball and splat! He was run over. One rabbit turned to the other and said, ‘That was bad luck. How many three-wheel cars do you get on this road?’ (Tibballs 2000: No. 193, 29) (p.57)

Simplified from Source: Ritchie, G. (2014). Logic and reasoning in jokes. European Journal of Humour Research, 2 (1), 50-60.

  • a hedgehog (n): a small mammal with needles on its back
  • a verge (n): an edge
  • headlights (n): bright lights at the front of a car
  • to line…up: to arrange something in a straight line
  • to scamper (v): to hurry
  • to curl up (v): to bend one's body into a circular shape
  • to pluck up (v): to raise [esp. courage]

Annotating arguments

Activity 10 Computer

The text below is annotated with html-like tags. These tags are matched in the Argument Visualizer. Opening and closing tags are used to show the start and finish points of each element.

Copy and paste the texts below in the Argument Visualizer Then, use the toggle buttons to hide or reveal the visualizations.

Text 1: Hungry monkey

<prem>The monkey is hungry. </prem> <prem>There is a banana. <hidden></hidden></prem><inductive></inductive><conc>The monkey will eat the banana. </conc>

Text 2: Professor X

<conc>Professor X is an efficient and effective teacher.</conc><prem>
<redherr>All his students enjoy his classes </redherr>according to the feedback given on the student feedback questionnaires.</prem>
<prem><misstat>Every student who attended the course in full received a grade A which is testimony of his expertise in teaching.</misstat></prem>
<prem>.<redherr>The professor not only holds a doctorate in physics but is also a polyglot and a polymath.</redherr></prem>
<prem><bandwagon>His course is always popular with students.</bandwagon></prem> <prem><misstat>Every course offered in the previous two years has seen enrolments meeting or exceeding the minimum number of students.</misstat></prem>
<prem><redher>To ensure he has enough energy, he always brings a cup of coffee to the classroom.</redherr></prem>
This is yet more evidence of his dedication to his students.
<prem><bandwagon>Finally, the Facebook page of Professor X has received thousands of “Likes”, a clear indication of votes of confidence in his teaching.</bandwagon></prem>

Evaluating long texts

Activity 11 Comprehension and analysis

Read the passage to answer the following questionss.

  1. What is the main message in paragraph 1?
  2. Do the title and paragraph have the same or different messages?
  3. What is the connection between the world`s first video camera feed and coffee?
  4. How many projects were inspired by coffee?
  5. Did Apple and NASA create a high-tech coffee maker?
  6. Is coffee the most popular drug in the world?
  7. Which two regions drink large amounts of coffee per person?
  8. Which two regions large numbers of top research output?
  9. Is there a connection between coffee and research output?
  10. Workers in which profession drink the most coffee?
  11. Is the evidence for this reliable?
  12. Does the article state that beer is more or less popular than coffee?
  13. Is the evidence for this reliable?
  14. When is the recommended time to drink coffee?
  15. Does the article recommend one or more cups per day?
  16. Each paragraph contains citations. Are these citations reliable?

Compare your answers with a friend.

Now you understand the meaning of the text, critically evaluate this argument.

Drinking coffee leads to scientific success

Coffee acts as a stimulus, guaranteeing increased research output and has become the keystone of many research laboratories with scientists harnessing its doping effects to function at their peak while benefiting from its antioxidant properties [1].

Caffeine, 1,3,7 trimethylxanthine (Crystalline xanthine alkaloid), causes the release of dopamine in the brain. The desire for a caffeine buzz spurred scientists in the University of Cambridge to upload the world`s first video camera feed in 1991 on the Internet. The camera sent images of the status of the Trojan room coffee pot to their laboratory so that they could check whether there was fresh coffee in the pot [2].

The desire for a perfect cup of coffee inspired another project. Former Apple and NASA engineers collaborated to create a high-tech coffee maker that brews a perfect coffee and includes features, such as thermostatic control, a QR reader and wifi [3]. Thus, coffee acted as a stimulus for research rather than a stimulant.

“Caffeine is the most widely used psychoactive substance in the world” [4] with a worldwide consumption in excess of 10 million tons per annum [5]. The USA and Scandinavia both ranked among the top coffee drinking nations per capita [6] and top scientific output per capita [7]. Given this established correlation between coffee drinking and research, it can be concluded that drinking coffee can lead to increased research output.

Based on a survey of 4700 American workers, scientists were found to drink the most coffee [8]. Given that coffee is the most popular drink and that scientists drink the most coffee, there are two plausible conclusions. Either scientists drink the most coffee as they crave popularity or scientists are popular and so drink coffee. Either way, the correlation between coffee drinking and scientists cannot be denied. 

As further proof, a Boolean search using Google [9] for “scientists and beer” results in 16 million hits while “scientists and coffee” produced over 58, million hits, which is almost 4 times more. Axiomatically, coffee is far more popular for scientists to drink than beer.

A chronopharmacological assessment of coffee intake concluded that as cortisol levels naturally spike around 9am, 1pm and 6pm, that the optimum time to drink coffee is between 9.30am and 11:30 [10], presumably assuming monophasic sleep and a standard circadian rhythm. The doping effect of caffeine can be harnessed throughout the working day to ensure that scientists are functioning at their peak.

The foundation of science may be based on Occam`s razor and the scientific method, but the foundation of the workday of scientists in based on coffee [11].

[1] A. Svilaas, A.K. Sakhi, L.F. Andersen, T. Svilaas, E.C. Strom, D.R. Jacobs Jr., et al. (2004). Intakes of antioxidants in coffee, wine, and vegetables are correlated with plasma carotenoids in humans. Journal of Nutrition, 134, 562–567.
[2] Coffee Cam. MIT Technology Review.  Available at: http://www.technologyreview.com/article/401059/coffee-cam/
[3] Kim, S. (29 September, 2012). Former Apple, NASA engineers make $11,111 coffee maker. ABC news. Available at: http://abcnews.go.com/blogs/business/2012/09/former-apple-nasa-engineers-make-11111-coffee-maker/
[4] Daly, J.W., Holmén, J., & Fredholm, B.B. (16 December 1998). Is caffeine addictive? The most widely used psychoactive substance in the world affects same parts of brain as cocaine. Lakartidningen, 95 (51-52), 5878-83.
[5] Butt, M.S. &  Sultan M.T. (2011). Coffee and its consumption: benefits and risks.  Critical Reviews in Food Science and Nutrition, 51, 363–373.
[6]  http://en.ilovecoffee.jp/posts/view/32
[7] Young, J. (2011, 1 November) The top 20 countries for scientific output
[8] Dunkin`Donuts and CareerBuilder survey
[9] www.google.co.jp
[10] Miller, S. (7 November, 2013). The scientifically best time to drink coffee. Available at: http://gizmodo.com/the-scientifically-best-time-to-drink-coffee-1460030914
[11] Blake, J. (2014). Drink coffee.  Post-it note. Top left filing cabinet drawer. Aizuwakamatsu: University of Aizu.

  • optimum (adj): best
  • caffeine (n): the chemical in coffee that is a stimulant
  • doping (n): adminstering drugs
  • a Post-it note. (n): a small sticky note that can be attached to books, desks, etc.
  • Scandinavia (n): Denmark, Norway and Sweden
  • a stimulant (n): a substance (e.g. drug) that raises activity levels in the body
  • a stimulus (n): an event or item that results in an action (e.g. ringing the bell for Pavlov's dog.

Activity 12 Vocabulary

Look up in a dictionary any words below whose meaning is unclear.

  • a truism (n): something that is true
  • a weakling (n): a weak person or a weak animal
  • Columbus's eggs (n): a brilliant idea or discovery that seems simple or easy after the fact
  • aversion (n): wanting to avoid
  • segregation (n): division
  • propagation (n): reproduction, e.g. having babies for humans
  • offspring (n): e.g. children for humans, puppies for dogs, etc

  • patent (adj): obvious
  • superficial (adj): surface level
  • restricted (adj): limited

  • to cease (v): to stop
  • to mate (v): to breed
  • to mingle: to mix
  • to prevail (v): to win
  • to succumb (v): to give in
  • to struggle (v): to fight

  • countless proofs: much evidence
  • Aryan blood: people with blood of European or Western Asia parents

Activity 13 Extended text

This text is included as a poor example of an argument that is full of fallacies. Your task is to find the flaws in the argument and not to fall victim to its persuasive rhetoric.

Critically evaluate the text below.

Mein Kampf Chapter 11 Nation and Race

There are some truths which are so obvious that for this very reason they are not seen or at least not recognized by ordinary people. They sometimes pass by such truisms as though blind and are most astonished when someone suddenly discovers what everyone really ought to know. Columbus's eggs lie around by the hundreds of thousands, but Columbuses are met with less frequently.

So men without exception wander about in the garden of Nature; they imagine that they know practically everything and yet with few exceptions pass blindly by one of the most patent principles of Nature's rule: the inner segregation of the species of all living beings on this earth.

Even the most superficial observation shows that Nature's restricted form of propagation and increase is an almost rigid basic law of all the innumerable forms of expression of her vital urge.Every animal mates only with a member of the same species.The titmouse seeks the titmouse, the finch the finch, the stork the stork, the field mouse the field mouse, the dormouse the dormouse, the wolf the shewolf, etc.

Only unusual circumstances can change this, primarily the compulsion of captivity or any other cause that makes it impossible to But then nature begins to resist this with all possible means, and her most visible protest consists either in refusing further capacity for propagation to bastards or in limiting the fertility of later offspring; in most cases, however, she takes Away the power of resistance to disease or hostile attacks.

This is only too natural.

Any crossing of two beings not at exactly the same level produces a medium between the lev el of the two parents. This means: the offspring will probably stand higher than the racially lower parent, but not as high as the higher one.consisting, it will later succumb in the struggle against the higher level. Such mating is contrary to the will of Nature for a higher breeding of all life.The precondition for this does not lie in associating superior and inferior, but in the total victory of the former.The stronger must dominate and not blend with the weaker, thus sacrificing his own greatness. Only the born weakling can view this as cruel, but he after all is only a weak and limited man; for if this law did not prevail, any conceivable higher development of organic living beings would be unthinkable.

The consequence of this racial purity, universally valid in Nature, is not only the sharp outward delimitation of the various races, but their uniform character in themselves. The fox is always a fox, the goose a goose, the tiger a tiger, etc. , and the difference can lie at most in the varying measure of force, strength, intelligence, dexterity, endurance, etc., of the individual specimens. But you will never find a fox who in his inner attitude might, for example, show humanitarian tendencies toward geese, as generally there is no cat with a friendly inclination toward mice.

Therefore, here, too, the struggle among themselves arises less from inner aversion than from hunger and love. In both cases, nature looks on calmly, with satisfaction, in fact. In the struggle for daily bread all those who are weak and sickly or less determined succumb, while the struggle of the males for the female grants the right or opportunity to propagate only to the healthiest. And struggle is always a means for improving a species' health and power of resistance and, therefore, a cause of its higher development.

If the process were different, all further and higher development would cease and the opposite would occur. For, since the inferior always predominates numerically over the best, if both had the same possibility of preserving life and propagating, the inferior would multiply so much more rapidly that in the end the best would inevitably be driven into the background, unless a correction of this state of affairs were undertaken. Nature does just this by subjecting the weaker part to such severe living conditions that by them alone the number is limited, and by not permitting the remainder to increase promiscuously, but making a new and ruthless choice according to strength and health.

No more than Nature desires the mating of weaker with stronger individuals, even less does she desire the blending of a higher with a lower race, since, if she did, her whole work of higher breeding, over perhaps hundreds of thousands of years, night be ruined with one blow.

Historical experience offers countless proofs of this. It shows with terrifying clarity that in every mingling of Aryan blood with that of lower peoples the result was the end of the cultured people. North America, whose population consists in by far the largest man part of who mixed but little with the lower colored peoples, shows a different humanity and culture from Central and South America, where the predominantly Latin immigrants often mixed with the aborigines on a large scale. By this one distantly, of racial mixture. The Germanic inhabitant of the American continent, who has remained racially pure and unmixed, rose to be master of the continent; he will remain the master as long as he does not fall a victim to defilement of the blood.

The result of all racial crossing is therefore in brief always the following:

  • lowering of the level of the higher race;
  • physical and intellectual regression and hence the beginning of a slowly but surely progressing sickness.
To bring about such a development is, then, nothing else but to sin against the will of the eternal creator. [abridged]

Audio texts

Activity 14 Listening

Critically evaluate the "we found a witch" scene.

Knowledge and application

Activity 15 Written analysis

Write a critical evaluation of the "Drinking coffee leads to scientific success" in Activity 12. Use the advice in Activity 1. Submit one-side A4 pdf of your analysis via ELMS. Ensure that you use logical terminology appropriately. Use short simple sentences or bullet points. Be clear and concise.

Activity 16

Evaluate the arguments critically in everything that you read and hear. You can practise critical and logical thinking every day. Share your logical analyses in the Unit forum and comment when/if you would like to.


Make sure you can evaluate the following items in arguments:

  1. conclusion, premises, reasoning, assumptions, formal and informal fallacies, and quality of evidence

Make sure you can explain the following concepts:

  1. paradoxes
  2. Loki's wager
  3. Sorites paradox

Running count: 108 of 108 logical concepts covered.