NN

To Susanna (384)
Your quotation from The Stanford Encyclopedia of Philosophy is correct: “A good argument is one whose conclusions follow from its premises; its conclusions are consequences of its premises.” The point is that an formally invalid argument DOES NOT follow from its premises.

Your arguments are not formally valid. There are two valid syllogism forms:
1) Modus Ponens – http://en.wikipedia.org/wiki/Modus_ponens
2) Modus Tollens – http://en.wikipedia.org/wiki/Modus_tollens

There are two formal logical fallacies for syllogisms:
1) Your first syllogism committed Affirming the Consequent – http://en.wikipedia.org/wiki/Affirming_the_consequent
2) Your second syllogism committed Denying the Antecedent – http://en.wikipedia.org/wiki/Denying_the_antecedent

Hope these help