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1.  Logic: The Science that Evaluates Arguments
◦ Logic teaches us to develop a system of methods and
principles to use as criteria for evaluating the arguments
of others to guide us in constructing arguments of our
own.

2.  The Nature of Arguments: Premises and
Conclusions
◦ An argument is a group of statements, one or more of
which (the premises) are claimed to provide support for,
or reasons to believe, one of the others (the conclusion).

3.  Premise Indicators and Conclusion Indicators
◦ Some typical conclusion indicators: therefore,
accordingly, entails that, etc.
◦ Some typical premise indicators: since, in that, seeing
that, etc.

4.  Typical structure of premises and conclusions:

5.  Arguments vs. Nonarguments
◦ At least one statement must claim to present evidence or
reasons.
◦ The alleged evidence must claim to support or imply
something.

6.  Simple Noninferential Passages: Basic
Nonarguments
◦ Warning
◦ Piece of advice
◦ Statement of belief or opinion
◦ Report
◦ Loosely associated statements
 Expository Passages: Proof vs. Elaboration

7.  Illustrations: Aid in Exemplification

8.  Explanations: “Why Something is the Case” vs.
“That Something is the Case”
◦ Golf balls have a dimpled surface because dimples
reduce air drag, causing the ball to travel farther.

9.  Conditional Statements by Themselves Are Not
Arguments
◦ If professional football incites violence in the home, then
we should reconsider giving widespread approval to the
sport.

10.  Deduction and Induction: Necessity vs. Probability
◦ Deductive arguments incorporate the claim that it is
impossible for the conclusion to be false if the premises
are true.
◦ Inductive arguments claim that it is improbable that the
conclusion be false if the premises are true.

11.  Common Types of Deductive Arguments: Based
on Mathematics, From Definition, Categorical,
Hypothetical and Disjunctive Syllogisms
◦ Example: Meerkats are members of the mongoose
family. All members of the mongoose family are
carnivores. Therefore, it necessarily follows that the
meerkat is a carnivore.

12.  Common Types of Inductive Arguments:
Prediction, Analogy, From Authority, Based On
Signs, Causal Inference
◦ Example: The meerkat is closely related to the suricat.
The suricat thrives on beetle larvae. Therefore, probably
the meerkat thrives on beetle larvae.

13.  Valid vs. Invalid Deductive Arguments
◦ Valid deductive arguments are arguments in which it
is impossible for the conclusion to be false given that
the premises are true.
◦ Invalid deductive arguments are arguments in which
it is possible for the conclusion to be false given that
the premises are true.

14.  Soundness: Validity plus all true premises
 Sound Argument = Valid argument + All true
premises
Example:
All flowers are plants.
All daisies are flowers.
Therefore, all daisies are plants.

15.  Strong vs. Weak Inductive Arguments
◦ Strong inductive arguments are arguments in which it is
improbable that the conclusion is false given that the
premises are true. In such arguments, the conclusion
does probably follow from the premises.
◦ Conversely, a weak inductive argument is an argument
in which the conclusion does not follow probably from the
premises, even though it is claimed to.

16.  Cogent Argument = Strong Argument + All true
premises
◦ Example: Every previous U.S. president was older than
40. Therefore, probably the next U.S. president will be
older than 40.

17.  Form as determinative of validity
◦ All valid arguments take this form:
All a are b.
All c are a.
All c are b.

18.  Creating a Substitution Instance
All a are b. All sporting events are engaging pastimes.
All c are a. All baseball games are sporting events.
All c are b. All baseball games are engaging pastimes.
This argument is a substitution instance of the
argument form. Any substitution instance of a valid
argument form is a valid argument.

19.  The Counterexample Method
1. Isolate the form
All migratory waterfowl are birds that fly south for the winter.
All geese are migratory waterfowl.
Therefore, all geese are birds that fly south for the winter.

20. 2. Construct a Substitution Instance with true premises
and a false conclusion
The form of the argument is
All a are b.
All c are a.
All c are b.

21.  This form is identical to the form we just
considered and is valid.
◦ Now consider an invalid argument form:
All a are b.
All c are b.
All a are c.

22.  Vertical Patterns: Conclusions subsequently
become premises
◦ The vertical pattern consists of a series of arguments
in which a conclusion of a logically prior argument
becomes a premise of a subsequent argument.

23.  Horizontal Patterns: When separate premises
independently support a conclusion
◦ The horizontal pattern consists of a single argument in
which two or more premises provide independent
support for a single conclusion. If one premise was
omitted, the other(s) would continue to support the
conclusion in the same way.

24.  Conjoint Premises: When separate premises
can only support a conclusion together
◦ These premises depend on one another so closely that
if one were omitted, the support that the others provide
would be diminished or destroyed.

25.  Multiple Conclusion: When a premise supports
more than one conclusion in a passage
◦ Although no single argument can have more than one
conclusion, we evaluate such passages as consisting of
two or more arguments, but we join the two conclusions
with a bracket.