Reason “Crime is common, logic is rare”

- Sherlock Holmes

Reason

There are many ways that human’s ‘use’ reason.

There are also many ways to use the term…

These prices are very reasonable.

She acted reasonably.

He used reason to win argument.

There was reason why she did that.

He had his own reasons for his decision.

What is ‘Reason”?

The way in which we try to make sense of the world using…

logic

rationality

comparison

judgment

experience

How do we “reason”?

Reason is something that we use whenever we make a decision.

Our reasoning mostly happens instinctively.

It is possible to train ourselves to reason consciously.

The more we think about our decisions, the more control we have over them.

Reason as Knowledge

One of the great attractions of reason as a source of knowledge, is that is seems to give us certainty.

Example: given that all human beings are mortal, and given that Socrates is a human being, it necessarily follows that Socrates is mortal.

premises: in logic, another word for ‘assumption’

given the assumption… the conclusion has to follow

Rationalism

Reason is the most important source of knowledge.

Deductive Reasoning

any form of reasoning that moves from the general to the particular

Example:All dogs are mammals. (general)

Fido is a dog.

Therefore Fido is a mammal. (particular)

Syllogism: a specific type of deductive argument (the example above is an example of a deductive argument)

Syllogisms

A syllogism consists of the following items:

1. 2 premises and a conclusion

2. 3 items, each of which occurs twice

3. quantifiers; such as ‘all’, ‘some’ or ‘no’

Belief Bias

This refers to the tendency we have to believe that an argument is valid simply because we agree with the conclusion.

enthymeme

an incomplete argument

Example: Jenny goes to Harvard, so she must be very intelligent.

Graham is a politician so he is probably lying.

What is missing???

Inductive Reasoning

an argument that moves from the particular to the general (opposite of deductive reasoning)

Inductive reasoning typically moves from the observed to the unobserved.

Example: Since apples have nourished me in the past, I assume that they will nourish me in the future.

Example: Since my neighbors dog has been friendly to me in the past, I am confident that he will not bite me today.

Think about this…

My dog, Fido, gets excited when I get his leash out, and seems to know that he is about to go for a walk. Do you think he is using inductive reasoning to predict what is going to happen in the future? Does this mean that he is able to reason?

Deduction & Induction Compared

Deduction Induction

Definition

Reasoning from general to particular

Reasoning from particular to general

Example

All metals expand when heated.

A is a metal.Therefore A expands when

heated.

Metal A expands when heated; metal B expands

when heated; metal C expands when heated.

Therefore all metals expand when heated.

Value

More certain, but less informative than induction

More informative, but less certain than deduction

More Important Terminology to

Consider…Vested Interest: when someone has a personal reason for an argument or possible a cause for suspicionBinary Thinking: looking at things as an “absolute” black or white situation.Rationalization: when we manufacture (create) bad reasons or arguments, simply for our own personal positionsLaws of Thought: the idea that logical reasoning cannot really be doubtedPrison of Consistency: when you take a position on something and find it difficult to change without “losing face”Lateral Thinking: thinking “outside the box” or non-traditional logic