A BRIEF LESSON IN LOGIC Principles of Reasoning and Argument
Modus
ponens is a Latin term meaning "in the mood of affirming";
modus
tollens means "in the mood of denying."
Modus Ponens(MP)
Modus Tollens(MT) Disjunctive Syllogism
(DS)
1. If P then Q
1.
If P then Q.
1.
Either P or Q.
2. P
2. Not Q.
2. Not P
3. Therefore, Q.
3.
Therefore not P.
3. Therefore, Q.
Fallacy of affirming the consequent: 1. If P then Q. 2. Q. 3. Therefore, P
Fallacy of denying the antecedent: 1. If P then Q. 2. Not P.
3.
Therefore, not Q.
Disjunctive syllogism. Deuteronomy 30:15-19
A
necessary condition is one that must
prevail before a second condition can occur.
A
sufficient condition is one that is
adequate for another condition to succeed.
The Law
of Identity.
Self
Refutation.
Contradictory statements are those that
necessarily
have the opposite truth values-one is true and the other false.
When we say that the propositions "All
S are
P" and "No S are P" are contraries, we mean that they cannot
both be true. At least one of them must be false (in fact, both may be
false.
Converse forms of
propositions are given the names A, E, I, and O: A = All S are P
(converse = AI
I P are S), E = No S are P (converse = No P are S), I = Some S are P
(converse
= Some P are S), and O = Some S are not P (converse = Some P are not
S). Note
that in each case, the converse simply switches the subject and
predicate terms
S and P. When you convert an E or I statement, the new statement is
logically
equivalent; that is, the converted statement will have the very same
truth
Appeal to pity.
Appeal
to the people.
Ad
hominem.
Genetic
fallacy.
Straw
man.
Red
herring.
Begging
the question.