 Aristotle often contrasts dialectical arguments with demonstrations. The difference, he tells us, is in the character of their premises, not in their logical structure: whether an argument is a sullogismos is only a matter of whether its conclusion results of necessity from its premises. The premises of demonstrations must be true and primary, that is, not only true but also prior to their conclusions in the way explained in the Posterior Analytics. The premises of dialectical deductions, by contrast, must be accepted (endoxos).