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| the organized body of knowledge, or science, that evaluates arguments. |
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| a group of statements, the purport of which is that some of them (the premises) should support, imply, provide evidence for, or make reasonable to believe another particular one of them (the conclusion). |
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| set forth the reasons for the conclusions; the conclusion is meant to follow from these reasons. |
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| those in which the premises really do support, imply, provide evidence for, or make reasonable to believe the conclusion |
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| those in which the premises do not in fact support, etc. the conclusion, even though the argument purports that they do so |
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thus
therefore
consequently
hence
so
it follows that
proves that
indicates that
*accordingly
implies that
*for this reason
as a result
we can infer
this means
entails that
implies that
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for
since
as
because
for the reason
follows from
after all
in light of the fact
*for the reason
assuming that
the reason is
inasmuch as
given that
in view of
granting that
seeing that |
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| the meaning-contents of statements. |
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When the arguer claims that it is impossible for the conclusion to be false given that the premises are true,
An argument is deductive if its purport is that it is impossible that its premises be true and its conclusion false. |
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When the arguer merely claims that it is improbable that the conclusion be false given that the premises are true.
An argument is inductive if its purport is merely that it is improbable that its premises be true and its conclusion false. |
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| if the argument employs such words as “necessarily,” “certainly,” or “absolutely,” it is usually best regarded as deductive. |
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| If expressions such as “probably,” “likely,” or “plausibly” are employed, the argument is usually best regarded as inductive. |
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| A deductive argument is valid if it is impossible for the conclusion to be false given that the premises are true. |
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| Invalid Deductive Argument |
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| If there is any possibility that the premises could all be true and yet the conclusion false, then the argument is invalid. |
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| A sound argument is a deductive argument that is valid and has all true premises. |
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| A cogent argument is an inductive argument that is strong and has all true premises. |
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| A categorical proposition is a proposition that relates two classes, or categories, denoted respectively by the subject term and the predicate term. |
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| The words “all,” “no,” and “some” are called logical quantifiers. |
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| The words “are” and “are not” are called copulas. |
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| Quality of a Categorical Proposition |
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| The quality of a categorical proposition is defined as affirmative if it affirms class membership (as do “All S are P” and “Some S are P”). The quality is negative if it does not affirm a class membership ( 'No S are P.' and 'Some S are not P.') |
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| Quantity of a Categorical Proposition |
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| The quantity of a categorical proposition is defined as universal if it makes a claim about every member of the S class (as do “All S are P” and “No S are P”) and particular if it makes a claim about just some (at least one) member of the S class (as do “Some S are P” and “Some S are not P”). |
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| Tradition or Aristotelian Sense |
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| If the propositions are taken to imply the existence of at least one member of the class denoted by their subject term “S,” and of at least one member of the class denoted by their predicate term “P,” then the proposition are being understood in the tradition or Aristotelian sense. |
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| If the propositions are not taken to imply the existence of at least one member of the class denoted by their subject term “S,” and of at least one member of the class denoted by their predicate term “P,” then the propositions are being understood in the modern or Boolean sense. |
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Conversion consists of simply switching the subject term with the predicate term while leaving the quality and quantity of the proposition unaltered.
Example: “All dogs are mammals”
--> Converse -->
“All mammals are dogs.” |
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| Logically equivalent claims for Converse |
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Obversion consists of both
(1) changing the quality of the proposition (leaving the quantity the same),
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(2) complementing the predicate term. |
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| Logically equivalent claims for Obversion |
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| The obverse of any categorical proposition, A, E, I or O, is logically equivalent to it. |
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Contraposition consist of both
(1) switching the subject with the predicate term (while leaving the quality and quantity of the proposition unaltered),
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(2) complementing both terms. |
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| Logically equivalent claims for Contraposition |
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| A and O Propositions are logically equivalent. |
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| To complement the predicate term, one typically attaches the prefix “non-“ to it. |
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