OPHL131 – Critical and Creative Thinking
Assignment 1

Maximum mark for this test: 60
(30% of total mark for this unit)


• Number your answers clearly.
• Give your answers in the order in which questions appear below.
• Where questions request examples, they must be included.
• Where questions require you to provide an explanation you should include all the relevant points you can think of, but avoid repetition and verbosity.

Please note that how your answers are written (spelling, punctuation, grammar, vocabulary, etc.) will be taken into account when they are marked.

1 – Define the following terms. Give your own example for each definition. (3 marks each, 12 marks total)

(a) Truth-value of an Assertion

(b) Argument

(c) Enthymeme

(d) Complex Argument

2 – Indicate which of these is:
(1 mark each, 6 marks total)

- an assertion (or series of assertions)
- an explanation
- an argument (do not include enthymemes)

(a) It is very important that you wear gloves while serving food.

(b) A rod will appear bent when partially submerged in water because the refractive index of water is greater than that of air.

(c) You should always show respect for your elders. They are both wiser and more virtuous than young people.

(d) The steak was past its use-by date. That must be why you got food poisoning!

(e) Edmund Hillary and Tenzing Norgay were the first people to reach the summit of Mount Everest. Ernst Schmied and Juerg Marmet were the second group to reach the summit.

(f) I saw the police chasing after him, so he must be a criminal.

3 – Identify which assertions are premises and which are conclusions in the following arguments. Remember that a single sentence may include multiple assertions. (1 mark each, 5 marks total)

(a) Everyone should learn to fish. It relaxes the mind, and allows one to survive in the wild.

(b) Money is not the most important thing in the world. That is why you should find work that is fulfilling, rather than lucrative. Then, even if you are poor, you will be happy.

(c) All pigs are animals that can whistle. Some animals who like mud are pigs. Thus, some animals who like mud can whistle.

(d) When one is dreaming, one doesn’t always know it. I don’t know whether I am dreaming now, so I might well be.

(e) An axe is a type of weapon, since ancient warriors used them. Lumberjacks use axes every day for work, hence some people are allowed to bring weapons to work.

4 – Complete the categorical syllogisms by adding the missing premise or conclusion. Make sure the completed syllogism is valid. (1 mark each, 4 marks total)

Premise 1: ……………………………………
Premise 2: All fish are sea creatures.
Conclusion: All tuna are sea creatures.

Premise 1: All drums are instruments that are played by hitting them.
Premise 2: …………………………………….
Conclusion: All drums are percussion instruments.

Premise 1: All students should strive to surpass their teacher.
Premise 2: Aristotle is a student.
Conclusion: ……………………………………

Premise 1: ……………………………………
Premise 2: Some wizards are old men.
Conclusion: Some wizards have grey beards.

5 – Analyse the following argument. Circle inference indicators, and bracket and number each statement. Draw an arrow diagram showing the structure of the argument. Then, rewrite it in standard form.
(6 marks)

Animals must be killed in order to produce meat, but killing animals causes them to suffer. So, producing meat causes animals to suffer. Therefore, one should only produce meat if it is for the greater good, since suffering should only be caused if it serves the greater good.

6 – Decide which paragraphs contain an argument and how many. Indicate whether these are simple or complex arguments. Identify the premises and conclusions (clearly distinguish between intermediate conclusions and final conclusions). (3 marks each, 12 marks total)

(a) Driving a fast car will hone your reflexes, but only if you don’t crash. Not crashing requires that you have good reflexes already, so only people who already have good reflexes will be able to hone them by driving a fast car.

(b) Some scholars claim that humans evolved from a common ancestor to the great apes. Others claim that humans were created directly by a god.

(c) All master thieves are sneaky, and sneaky people are not to be trusted. Sarah is a master thief, so she is also sneaky and untrustworthy.

(d) Animals should not be harmed unnecessarily because they can suffer. Humans should not be harmed for the same reason.

7 – Write a categorical statement (using all, no, or some) that matches the shading of each Venn diagram. (1 mark each, 3 marks total)




8 – Match each of the categorical arguments to one of the Venn Diagrams below. Explain whether the argument is valid or invalid. (3 marks each, 12 total)

(a) Premise 1: All jet planes are vehicles.
Premise 2: All cars are vehicles.
Conclusion: All jet planes are cars.

(b) Premise 1: No mammals are birds
Premise 2: All cats are mammals.
Conclusion: No cats are birds.

(c) Premise 1: Some liars are lawyers.
Premise 2: All lawyers play lyres.
Conclusion: Some liars play lyres.

(d) Premise 1: No lemons are sweet fruits.
Premise 2: No sweet fruits are sour fruits.
Conclusion: Some lemons are sour fruits.




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