Unit 1 – Foundations of Reason and Logic Section 1 – Reasoning about Reasoning

What is Reasoning? We all have to make decisions about what to believe and how to act Some of our questions are more personal and practical: ? Whom should I invite to formal? What will I do after completing high school?

Some questions involve our relationship with other and the world: Is it right to tell a lie? ? Why should I conserve energy?

Other decisions involve questions that are more philosophical: Can we truly know anything? ? Is the a god? .

So… What is Reasoning?! . Given the importance of reasoning we will begin to explore: The nature of reasoning Good reasoning from bad Our limits of reasoning

However, reasoning is not just thinking about ourselves Its about thinking in accordance with standards of reasoning and being on guard against; in our thinking.

Why is good reasoning important? . More informed, well thought out course of action $$$ is spent on advertising, which can be manipulative Help us assess claims made in the media Identify information that is credible and use it to our benefit Defend our beliefs and have them hold up scrutiny Why things are the way they are

General Principles of Reasoning . In his works he identified some general principles of logic and founded a branch of reasoning that we call formal logic Dedicated to the study of deductive arguments

Since his time many philosophers have attempted to build on his ideas by further defining laws of thought that are considered fundamental to the reasoning process Law of ___________ However, prior to understanding these laws we must first understand __________________

Proposition: _________________________________________ _________________________________________ Questions and commands are not propositions because we do not label them true or false Here are some examples The room is messy – true sometimes The shape of the earth is close to the shape of a sphere The moon is made of cheese – false 5 is a prime number – true always Capital punishment is never justified – up for debate

Law of identity States that: _________________________________________ _________________________________________ Whatever the thing is, it is what it is and does not have alternate identity or multiple identities So fundamental to our thinking is the view that something cannot be both what it is and at the same time and in the same respect, other than what it is

Law of non-contradiction States that: _________________________________________ _________________________________________ _________________________________________ Thus contradiction occurs when a proposition is held to be both true and false Example If you believe, today is Wednesday and today is not Wednesday at the same time (eastern standard) and in the same respect (not today is Wednesday but it feels like Tuesday) then you hold a contradiction.

Law of the excluded middle States that: _________________________________________ _________________________________________ _________________________________________ Example “It is raining.” Depends on the time and place to which we are referring. Thus the proposition may be true on July 23 in Toronto but not in Montreal or on July 23 but not on July 24 It is either raining or its not – there is no middle ground

Recap Using the example of a pencil, the laws work in this way: This pencil (A) must be this pencil (A)--in philosophical terms, this is called a tautology, which is something which is true by definition If this is a pencil (A), it cannot also not be a pencil (not A) at the same time It is either true that this thing is a pencil or it is not true that this thing is a pencil. It can't be a little bit true and a little bit false

The Principles of Sufficient Reason States that: _________________________________________ _________________________________________ There are several different versions of this principle For every entity X, if X exists, then there is a sufficient explanation for why X exists For every event E, if E occurs, then there is a sufficient explanation for why E occurs For every proposition P, if P is true, then there is sufficient explanation for why P is true

Ockham’s Razor Ockham stated that: _________________________________________ _________________________________________ Example You tell your teacher you don’t have your textbook because aliens took it and they went back home Your teacher is faced with two choices Believe or not Based on Ockham’s razor your teacher will reject choice 2 based on reasoning that your lose can be explained without aliens – that is, without adding entities (aliens beyond necessity)