In the mood/figure technique for evaluating categorical syllogisms why is the existential fallacy limited to only one required condition?

In the mood/figure technique for evaluating categorical syllogisms why is the existential fallacy limited to only one required condition?
In Venn diagrams for categorical syllogisms why is it sometimes important to diagram universal before particular premises?
Why is a categorical syllogism invalid if the middle term is not distributed at least once?
What are the comparative advantages and disadvantages of: a) Mood/Figure technique; b) Truth tables; c) Natural Deduction?
How are the following three logical operations related: a) Contraposition; b) modus tollens; c) Transposition?
What are some of the problems in employing the propositional calculus for translation?
Is a categorical syllogism valid if only Rule 5 is broken? (refers to Rule 5 in section 5.3)
When is a categorical syllogism enthymematic?
Can the rules for the categorical syllogism (section 5.3) be applied in the case of Sorites?
What is the difference between the Rules of Implication and the Rules of Replacement?