Introduction to Arguments 8/29/13
1) Find conclusion
2) Locate explicit premises
3) Locate any implicit premises
Explicit premise: Marijuana is less dangerous than alcohol
Explicit premise: Alcohol is legal
Implicit premise (not given, have to come up with): Everything less dangerous than
alcohol should be legal
Conclusion: Marijuana should be legal
1) Deductive Arguments
A. Valid or Invalid
B. Sound or not sound
A valid argument means that if the premises are true, then the conclusion
must be true. It means the argument is in the correct form. (Although the
conclusion may be true, the premises might not be true)
Example: Premise: I gazed into my crystal ball and determined that there are
27 students in this class
Conclusion: There are 27 students in this class
Although the conclusion is true, the premise is not true.
A sound argument is a valid argument with true premises.
Example of a deductive argument:
Premise: It is sunny in Miami
Premise: If it is sunny in Miami, I will not have an umbrella.
Conclusion: I will not have an umbrella.
Validity vs. Truth
Validity: A property of arguments
Truth: A property of statements
To say that a statement is valid does not make sense logically. That is like