The main form of inference in traditional logic is the syllogism. A categorical syllogism is the inference of one categorical proposition, the conclusion, from the other, the premise. Each premise, of which there are two, must have one term in common with the conclusion and one term in common one term in common with each other. It must be understood that not all syllogisms are valid. A valid syllogism is a syllogism where the form of the premises actually lead to, or infer, a true conclusion.
Some forms lead to invalid conclusions.
Just because a certain form is established, and it appears syllogistic, the conclusion may not be a consequent of the premises. This distinction strikes at the heart of understanding traditional logic, indeed all logic. The form of a syllogism will, by the relations existing between it's constituent propositions, lead to consistent results. If it is a valid syllogism, when you put in true premises, you will receive a true conclusion. If you substitute false premises then you will receive false conclusions.