1. Chapter 3 Philosophy: Questions and theories
Logic
Chapter 3
Philosophy: Questions and theories

2. What is Logic?
Logical arguments consist of one or more claims or premises and a conclusion arranged in such a way that the premises are supposed to support the conclusion
E.g.: All smokers risk getting lung cancer. Alice is a smoker. Therefore, Alice risks getting lung cancer.
Premise 1 : All smokers risk getting lung cancer.
Premise 2: Alice is a smoker.
Conclusion: Alice risks getting lung cancer.

3. The Philosopher’s Approach to Logic
Logic involves two forms of reasoning: deduction and induction.
Deduction: goes from big picture to little picture/ general to specific
All cats are mammals
My pet is a cat
Therefore my pet is a mammal
For a good deductive argument you must have the premises as true and the argument must be valid
The premises must logically entail the conclusion

4. Induction: the process of observing particular things and making generalizations – drawing general conclusions
Swan 1 is white
Swan 2 is white
Swan 3 is white
Swan 1000 white
Therefore, all swans are white
Inductive arguments differ from deductive arguments in that their premises are supposed to support but not logically entail their conclusion
They are not deductively valid, the premises justify the conclusion

5. General
Particular
Deduction
Induction

6. What Philosophers Have Said
Aristotle contributed to the logical thought with the three laws of thought
The law of non-contradiction say something cannot be said both to be and not to be at the same time and in the same respect
E.g.: If the statement, “Tom exists,” is true, it cannot also be false.
The law of the excluded middle says that something must either be or not be
E.g.: The statement, “Tom exists,” must either be true or not true. There is no middle.
The law of identity says that something is what it is
E.g.: To say that Tom is Tom and Sasha is Sasha is true while to say that Tom is Sasha is untrue.

7. Francis Bacon (17th century)
Although modern logicians have developed systems that involve more than simply true or false possibilities, Aristotle’s laws still serve as primary tools for mathematics.
Francis Bacon (17th century)
Emphasized inductive reasoning as a tool of science and became the foundation of the scientific method.
19th century George Boole
Developed Boolean/symbolic logic and used numbers and algebraic equations to represent chains of reasoning

8. How Philosophers Have Said It
An argument is a series of statements that consist of a premise or premises and a conclusion that follows from the premises.
A premise is a factual statement or proposition.
An argument is a response to a question and never opens with it or a command
Arguments start with statements that can be true or false.
Questions and commands are neither
Logical consistency means that the statements do not contradict each other to create a logical contradiction

9. A syllogism is a basic form of argument introduced by Aristotle and contains two premises and a conclusion
All humans are mortal (major premise)
I am human (minor premise)
Therefore I am mortal (conclusion)
“All” is a quantifier
Validity refers to the correctness of the reasoning and truth refers to the truth of the contents
All humans are immortal
Socrates is human
Therefore, he is immortal
Despite the truth of these statements, the argument is valid as the conclusion follows from the
Deductive reasoning is either valid or invalid but inductive arguments are reliable or weak
Logic is concerned with a form of argument and whether this form and the reasoning is correct