PHIL2642 Lecture Notes
Week 1: Introduction to Critical Thinking + Course Outline
• Week 2;
o Premises
• Week 3;
o Deduction Continued
• Week 4;
o Definitions and Philosophical Analysis
• Week 5;
o Induction
• Week 6;
o Induction, Analogy & Testimony
• Week 7;
o Abduction
• Week 8;
o Causal Arguments
• Week 9;
o Science, Pseudo-‐Science & Non-‐science + ‘Intelligent Design’ Case Study
• Week 10;
o Probabilistic Reasoning
• Week 11;
o Fallacies
• Week 12;
o More Fallacies
• Week 13;
o Practice Exam
Week 2 (First week of Content): Conditionals and Deduction
• Arguments;
o Premises o Conclusion
• Claims
• Explanations
o Explanandum (that which needs to be explained) o Explanans (that which contains the explanation)
• Conditionals;
o Statements that do not suggest one thing causes another à If P then Q claims;
§ If you are bigger than Arnie then you are bigger than me.
§ If the dam levels are higher then it rained.
• Sufficient condition [P]
PHIL2642 Lecture Notes
o For the standard form of conditional “If P then Q”, the sufficient condition is P.
o Sometimes called the “antecedent”.
§ E.g. If you are a father then you are a parent.
§ If you are a police officer then you are allowed to break the law.
• The sufficient condition comes after the ‘if’ and before the ‘then’, so it is “you are a police officer.”
§ If an asteroid hits earth tomorrow, everyone will die tomorrow.
• It is “an asteroid hits earth tomorrow”.
• Necessary condition [Q]
o For the standard form of conditional “If P then Q”, the necessary condition is Q.
§ If you’re a police officer then you are allowed to break the law.
• It is “you being allowed to break the law.”
§ If an asteroid hits earth tomorrow, everyone will die tomorrow.
• It is “everyone will die tomorrow”.
• Equivalent forms of conditionals o If P then Q:
§ If you are a father, then you are a parent
§ If it is more expensive than Point Piper then it is more expensive than Marrickville.
§ These also mean;
• P is sufficient for Q
• Q is necessary for P
• Q if P
• P only if Q
• Only if Q, then P
• How to figure out which is conditional/necessary? This must be learnt.
• “All”, “Every” and “Only” Generalisations
o ‘A’ and ‘B’ stand for objects or events and ‘F’ and ‘G’ stand for properties.
• Generalisations
o All members of the board are bald.
o All numbers greater than 7 are greater than 2.
• Common Mistakes
o ‘All’ and ‘only’ claims are not equivalent.
§ All fathers are parents.
§ Only fathers are parents. ß Wrong.
• Counterexamples to conditional claims and generalisations
o A thing, event or state of affairs in which the sufficient condition is true but the necessary condition is false.
§ If it is an ant, it is smaller than an elephant,
• Counterexample must demonstrate an ant bigger than an elephant.
§ If it is a triangle, then its angle sum is 180 degrees.
• No counterexample (True conditional claim).
PHIL2642 Lecture Notes
• Practice questions on conditionals
o You would be a troublemaker only if you did annoying things.
§ If you are a troublemaker, then you do annoying things.
o Mark goes to the movies only if Star Wars is showing.
§ If Mark goes to the movies then Star Wars is showing.
• Sufficient cond; Mark goes the movies.
• Necessary cond; Star Wars is showing.
o Being coloured is necessary for being red.
§ If it is red, then it is coloured.
• Sufficient con; Being red
• Necessary cond; being coloured.
o All children are whining brats.
§ If it is a child then it is a whining brat.
• Sufficient cond; It is a child
• Necessary cond; whining brat.
• Deduction
o Not all arguments are deductive.
§ The price of gold has risen steadily over the past year.
o Deductive arguments are those in which the truth of the premises is intended to guarantee the truth of the conclusion.
• Soundness
o It must possess 2 features in order to be a faultless deductive argument.
1. It must have only true premises.
2. The truth of those premises must guarantee the truth of the conclusion.
o We can see these 2 demands more generally as;
• It must have good (True) content in its premises.
• It must have good (Truth –preserving) form.
• Validity & Invalidity
o An argument is valid if the truth of the premises guarantees the truth of the conclusion.
• If I drink Fanta I have the strength of 10 men.
• I’m drinking Fanta, therefore I have the strength of 10 men.
• Whilst this argument is false, it is valid as the premise guarantees the conclusion.
• Valid if it Affirms the Sufficient or Denies the Necessary:
• Aff Suff
• Den Nec.
• Otherwise invalid.
o An argument is invalid if, assuming the premises are true, the conclusion might not be true. So it is possible for the premises to be true and the conclusion to be false.
• Everyone that drinks beer is an adult.
• à If you drink beer then you are an adult.
PHIL2642 Lecture Notes
• Tom is an adult, therefore he drinks beer.
• This is invalid.
• Conditional deductive arguments;
o Forms;
• Affirming the sufficient condition (valid):
• If there is a baboon in your tent, you shouldn’t go into your tent.
• There is a baboon in your tent.
• Therefore, don’t go in there.
• Denying the sufficient condition.
• Affirming the necessary condition.
• Denying the necessary condition (valid).
• If P then Q.
• It’s not the case that Q.
• Therefore it’s not the case that P.
• E.g. If I was a teenager in the 80’s, then I own a copy of Michael
Jackson’s “Thriller”.
o I do not own a copy of “Thriller”.
o Therefore, I was not a teenager in the 80’s.
Week 3: Deduction Continued
• Denying the sufficient condition.
o If there is a tiger at the zoo, then I’ll go to the zoo.
o Next premise;
§ There is no tiger at the zoo.
o Conclusion;
§ Therefore, I won’t go to the zoo à Invalid as the premises don’t guarantee the conclusion.
• Conditional arguments of many forms;
o Only snobs do not watch reality TV.
§ If you do not watch reality TV, then you are a snob.
§ You do watch reality TV.
§ Therefore, you are not a snob.
• Denying the sufficient.
o Only idiots think that Morocco is in Europe.
§ If you think that Morocco is in Europe, then you’re an idiot.
§ Dave thinks that Morocco is in Europe.
§ Therefore, Dave is an idiot.
• Affirming the sufficient condition. Valid.
o You will be punished if you stole from the shops.
§ If you stole from the shops, then you will be punished.
§ You did not steal from the shops.
