Syllogistic fallacies are formal fallacies that occur in syllogisms. Two "dicto simpliciter" fallacies can occur in statistical syllogisms. For this task Aristotle used the tool of deductive reasoning in the form of syllogisms. Note that categorical syllogisms have elements traditionally called middles, predicates, and subjects. On dialectic, he discusses philosophy, syllogisms, and definitions. The fallacy of four terms also applies to syllogisms that contain five or six terms. In the "Prior Analytics", Aristotle identifies valid and invalid forms of arguments called syllogisms. The "dictum de omni" is the highest principle of affirmative syllogisms. This table shows all 24 valid syllogisms, represented by Venn diagrams. It is also possible to use graphs (consisting of vertices and edges) to evaluate syllogisms. The similar syllogisms share the same premises, just written in a different way. Medical syllogisms are revolved by means of experience. The following table shows all syllogisms that are essentially different.