Does transposition of the premises preserve validity in categorical syllogisms?

What methods for determining the validity of a categorical syllogism are there?


  • The argument must have exactly three terms.
  • Every term must be used exactly twice.
  • A term may be used only once in any premise.
  • The middle term of a syllogism must be used in an unqualified or universal sense.

What makes a categorical syllogism invalid?

If both of the premises are particular (they talk about particular individuals or “some” members inside or outside a particular class, and so can’t be converted into conditionals), then the syllogism will be invalid.

What does the validity of syllogism depend on?

This method of differentiating syllogisms is significant because the validity of a categorical syllogism depends solely upon its logical form. Remember our earlier definition: an argument is valid when, if its premises were true, then its conclusion would also have to be true.

What are the six rules for validity for a syllogism?

There are six rules for standard-form categorical syllogisms:

  • The middle term must be distributed in at least one premise.
  • If a term is distributed in the conclusion, then it must be distributed in a premise.
  • A categorical syllogism cannot have two negative premises.

What makes a syllogism valid?

A syllogism is valid (or logical) when its conclusion follows from its premises. A syllogism is true when it makes accurate claims – that is, when the information it contains is consistent with the facts. To be sound, a syllogism must be both valid and true.

What are the valid categorical syllogisms?

All categorical syllogisms have what is called a “mood” and a “figure.” Mood: The mood of a categorical syllogism is a series of three letters corresponding to the type of proposition the major premise, the minor premise, and the conclusion are (A, E, I, or O).

What are the characteristics of categorical syllogism?

Rules of Categorical Syllogisms

  • There must exactly three terms in a syllogism where all terms are used in the same respect & context. …
  • The subject term and the predicate term ought to be a noun or a noun clause. …
  • The middle term must be distributed at least once in the premises or the argument is invalid.

Can any standard for categorical syllogism be valid that contains exactly three terms each of which is distributed in both of its occurrences?

No, such a syllogism cannot be valid. If each of the three terms were distributed in both of its occurrences, all three of its propositions would have to be E propositions, and the mood of the syllogism would thus be EEE, which violates Rule 4, which forbids two negative premises.

How many valid categorical syllogisms are there?

Valid syllogistic forms
In syllogistic logic, there are 256 possible ways to construct categorical syllogisms using the A, E, I, and O statement forms in the square of opposition. Of the 256, only 24 are valid forms.

Could there be such a thing as an invalid premise?

If an argument has all true premises and a false conclusion, then it is invalid.

When diagramming a categorical syllogism with a universal premise and a particular premise Why is it important to diagram the universal premise first?

If one of the premises is a universal proposition, diagram it first. (If both premises are universal, it does not matter which one you diagram first.) This is because you want to eliminate any place where an x, which represents a particular proposition, cannot go.

When an argument is valid if its premises were true its conclusion would be true too?

A sound argument is both valid and has all true premises. Since a sound argument is valid, it is such that if all the premises are true then the conclusion must be true. Since a sound argument also has all true premises, it follows that a sound argument must have a true conclusion. 8.

Can an argument with inconsistent premises be valid?

Yes. An argument with inconsistent premises is valid, regardless of what the conclusion is. If an argument has inconsistent premises, then it is impossible for all the premises to be true at the same time; hence it is impossible for all the premises to be true while the conclusion is false.

Do all valid arguments preserve truth?

If all your premises are true and you make a valid argument from them, it must be the case that whatever conclusion you obtain is true. (We shall see below, however, that valid arguments do not necessarily preserve truth value: it is entirely possible to argue validly from false premises to a true conclusion).