Valid Patterns of Categorical Syllogism

Theorem
The following categorical syllogisms are valid:


 * $\begin{array}{rl}

\text{I} & AAA \\ \text{I} & AII \\ \text{I} & EAE \\ \text{I} & EIO \\ \end{array} \qquad \begin{array}{rl} \text{II} & EAE \\ \text{II} & AEE \\ \text{II} & AOO \\ \text{II} & EIO \\ \end{array} \qquad \begin{array}{rl} \dagger \text{III} & AAI \\ \text{III} & AII \\ \text{III} & IAI \\ \dagger \text{III} & EAO \\ \text{III} & EIO \\ \text{III} & OAO \\ \end{array} \qquad \begin{array}{rl} \S \text{IV} & AAI \\ \text{IV} & AEE \\ \dagger \text{IV} & EAO \\ \text{IV} & EIO \\ \text{IV} & IAI \\ \end{array}$
 * \text{I} & AAI \\
 * \text{I} & EAO \\
 * \text{II} & EAO \\
 * \text{II} & AEO \\
 * \text{IV} & AEO \\

In the above:


 * $\text{I}, \text{II}, \text{III}, \text{IV}$ denote the four figures of the categorical syllogisms


 * $A, E, I, O$ denote the universal affirmative, universal negative, particular affirmative and particular negative respectively: see Shorthand for Categorical Syllogism


 * Syllogisms marked $*$ require the assumption that $\exists x: S \left({x}\right)$, that is, that there exists an object fulfilling the secondary predicate


 * Syllogisms marked $\dagger$ require the assumption that $\exists x: M \left({x}\right)$, that is, that there exists an object fulfilling the middle predicate


 * Syllogisms marked $\S$ require the assumption that $\exists x: P \left({x}\right)$, that is, that there exists an object fulfilling the primary predicate