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### Informal logic

Informal logic deals with operations of thinking that are indirectly related to reasoning

### Genus of a term

A genus of a term is a term that is more general, broad, or abstract then the original term and includes it

### Species of a term

A species of a term is a term that is more specific, narrow or concrete than the original term and is included by it

### Extension of a term

The extension of a term is the sum of all the individual objects described by it

### Intension of a term

The intention of a term is the sum of all the common attributes denoted by the term

### Self-supporting statement

A self-supporting statement is a statement whose truth value can be determined from the statement itself

### Tautology statement

A tautology is a statement which is always true because of its logical structure

### Supported statement

A supported statement is a statement whose truth value depends on evidence or information from outside itself

### Implication

Two statements are related by implication if the truth of one requires the truth of the other

### Independent statements

Two statements are independent if the truth of falsity of one has no effect on the truth or falsity of the other

### Real disagreement

A real disagreement is an actual inconsistency between two statements: they cannot both be true at the same time

### Verbal disagreement

A verbal disagreement is a misunderstanding due to differing definitions for one or more words

### Subject of a statement

The subject of a statement is the term being described, or about which something was asserted

### Quantity of a statement

The quantity of a statement is the scope of its claim about the extension of the subject: universal (entire extension) or particular (partial)

### Quality of a statement

The quality of a statement is the positive or negative nature of its claim about the subject:affirmative (asserts something) or negative (denies something)

### Square of opposition

the square of opposition is a diagram of the basic relationships between statements with the same subject and predicate

### Contrary statements

Two statements are contrary if and only if they can both be false but cannot both be true

### Subcontrary statements

Two statements are subcontraries if and only if both can be true but both cannot be false

### Subimplication

Subimplication is the relationship between a universal and particular statement of the same quality, in which the truth of the universal necessitates the truth of the particular

### Superimplication

Superimplication is the relationship between a universal and particular statement of the same quality

### Argument

An argument is a set of statements, one of which appears to be implied or supported by the others

### Conclusion of an argument

The conclusion of an argument is the statements which appears to be implied by the other statements in the argument, which are called premises

### Categorical syllogism

A categorical syllogism is a deductive argument consisting of three statements in categorical form that together use only three terms, called the major, minor, and middle

### Major term

The major term of a syllogism is the predicate of the conclusion and is used in one premise

### Schema of a syllogism

The schema of a syllogism is a representation of it, having statements in standard order with standard abbreviations of its terms

### Mood of a syllogism

The mood of a syllogism is a three-letter description of the types of categorical statements it contains when arranged in standard order

### Figure of a syllogism

The figure of a syllogism is a number from 1 to 4 identifying the placement of its middle term

### A valid syllogism

A syllogism is valid if the conclusion is necessarily true given that the premises are true

### Counterexample of a syllogism

The counterexample of a syllogism is a syllogism of the same form as the original, but with obviously true premises and false conclusion, in order to show the original to be invalid

### Distributed term

A distributed term is a term that, within a statement, refers to all the members of its class

### Immediate inference

The immediate inference is a statement which can be inferred directly from another statement

### Converse of a statement

The converse of a statement is a statement that reverses the subject and predicate. it is only valid for E and I

### Obverse of a statement

The obverse of a statement is a statement of the opposite quality with a negated predicate. It is valid for all statements

### Complement of a term

The complement of a term is the set of all terms not included in the given term. Thus the complement of the term P is non-P

### Contrapositive of a statement

The contrapositive of a statement is a statement that reverses and negates both the subject and predicate of the original. It is valid for A and O

### Enthymeme

An enthymeme is an arguement in which a statement is unstated and assumed. Specifically, it is a syllogism with one assumed statement

### Hypothetical

A hypothetical is a statement that affirms an outcome based on a condition. It has the form If P then Q

### Puere hypothetical syllogism

A pure hypothetical syllogism is an argument that uses only hypothetical statements

### Antecedent of a hypothetical statement

The antecedent of a hypothetical statement is the condition, the part following the "if." The consequent is the result of the condition, the part after the "then"

### The Latin phrase non sequitur

The Latin phrase non sequitur means "it does not follow"; i.e., that an arguement is invalid

### Fallacy of a distraction

A fallacy of a distraction is an argument that confuses the issue by pointing to information that is actually irrelevant to the conclusion

### Fallacies of ambiguity

Fallacies of ambiguity are arguments that confuse the real issue with multiple, vague, or otherwise uncleat meanings

### Fallacy of the accent

The fallacy of the accent alters the meaning of a statement through changed emphasis

### Fallacies of form

Fallacies of form are arguments that fail to establish their conclusions because of a weakness in logical structure

### Post hoc ergo propter hoc

Post hoc ergo propter hoc is improperly assuming that a sequence in time implies a cause and effect

### A complex question

A complex question is a question crafted to exclude any possible legitimate response