The classical first-order logic that we briefly covered in Chapter 26, is not a sufficient tool for use in medicine and also has some other shortcomings. Consequently, it must be extended, changed, amended, or abandoned. In this section, we shall address some of these concerns.Classical first-order logic has emerged as the first system of modern logic, and as such, it has enjoyed extensive study and development. It is therefore usually identified with logic itself. Its principles, theorems, and laws are believed to be irrefutable and eternal truths. There are those who even maintain that "Dictators may be powerful today, but they cannot alter the laws of logic, nor indeed can God even do so" (Ewing, 1940, 217). This claim reflects a widespread error that we encounter not only in everyday life, but also in most scientific disciplines. However, in what follows we shall show that classical logic and its laws are not the final word.