Formal vs. Informal Validity Worksheet
Consider the following arguments and circle (or highlight) all that apply
(1) If it is raining, the streets are getting wet. It is raining. Therefore, the streets are getting wet.
(a) This argument is valid.
(b) This

Formal vs. Informal Validity
What Logic is About
Logic, on one way of thinking about it, is the
study of how to figure out which arguments
are formally valid.
But what the heck does that mean?
Formal Validity
Consider the following argument:
(P1) If m

Conditionals and Negation
Negation
Negation
One important sentential connective found in English that I
didnt mention last time was not or it is not the case that.
We will call not or it is not the case that a sentential
connective even though, unlike t

Translating English Conditionals Worksheet
Use propositional variables and sentential connectives to
translate the following English sentences into logical
formulas. Your translations should bring out as much of
the logical structure of these sentences as

An Introduction to Proofs
Symbolizing Arguments
Symbolizing Arguments
Consider the following argument once again:
(1) If it is raining, the streets are getting wet
(2) It is raining
Therefore, the streets are getting wet
If we put the premises of this arg

What is an Argument?
The Monty Python Definition of An
Argument
An argument is a connected series of
statements intended to establish a definite
proposition.
Our Official Definition of An
Argument
An argument is a collection of
premises intended to lend

An Introduction to Propositional Logic
English Sentences and Propositions
English Sentences and Propositions
Some English sentences express truth-evaluable
claims about the world and some do not.
E.g. the sentences Earth is the third planet
from the Sun

Modus Tollens and Double Negation
Modus Tollendo Tollens
An Example
Consider the following argument:
(1) If it is raining, the streets are getting wet.
(2) It is not the case that the streets are getting wet.
(3) Therefore, it is not the case that it

The Rule of Assumption and Conditional
Proof
The Rule of Assumption
A Problem
p -> p
How do we prove this?
The Rule of Assumption
A: At any point, one may write down any
sentence that one pleases, provided that one
keeps due account of the fact that th