Philosophers in the Enlightenment era would come up with various new means to popularize ideas. Denis Diderot conceived the first encyclopedia in this period, which was an attempt to systematize all world knowledge in an accessible way. But also, in another innovation, Voltaire would offer as a refutation of the optimistic philosophy of Leibniz -- which held that "this is the best of all possible worlds" -- a new form of philosophical argument: the extended comedy (Cathcart and Klein, 17). Voltaire's short book Candide is essentially an extended refutation of Leibniz's view of God (or perhaps any view of God), but it makes its points through satirical humor. In some sense, Thomas Cathcart and Daniel Klein are following in the footsteps of Voltaire by attempting to shed light on philosophical ideas through the medium of humor in their work Plato and a Platypus Walk Into A Bar. However, it is worth noting that their methodology also combines Diderot's encyclopediac approach: the book attempts to be a basic introduction to the essential concepts of philosophy, but explores these concepts by use of jokes.
A useful entry into Cathcart and Klein's work is provided by their discussion of the somewhat forbidding topic of epistemology. Their joking tone provides a definition of this very concept which makes it clear what is at stake: "How do you know the stuff you think you know? Take away the option of answering 'I just do!' And what's left is epistemology." (Cathcart and Klein, 52). Obviously epistemology is basic to any Enlightenment-inspired enterprise: when Diderot constructed his first encyclopedia, it was done on the basis that the knowledge being collected in this format was actually reliable. There were plenty of philosophical schools that existed before the Enlightenment: obviously the entirety of Western philosophy in the medieval period was essentially based on the worldview of Christianity, whereas earlier philosophers like Pythagoras had endorsed various metaphysical beliefs that were opposed by Christianity, such as a belief in reincarnation. Cathcart and Klein acknowledge this by noting that the epistemological question "in the Middle Ages…boiled down to whether divine revelation trumps reason as a source of human knowledge or vice versa" (Cathcart and Klein 53). However the knowledge of the Enlightenment was not likely to endorse these sorts of beliefs about what happens after death, on the precise basis that we have no actual evidence regarding what happens after death: this is a basic epistemological stance, which reveals that we do not "know" but rather "believe" in various alternatives about what happens to a person after death. In some sense, therefore, knowledge comes to us by way of doubt. This is a point that Cathcart and Klein make usefully in their discussion of Descartes as they introduce the concept of epistemology:
Descartes arrived at the cogito through an experiment in radical doubt to discover if there was anything he could be certain of; that is anything he could not doubt away. He started out by doubting the existence of the external world. That was easy enough. Perhaps he was dreaming or hallucinating. Then he tried doubting his own existence. But doubt as he would, he kept coming up against the fact that there was a doubter. Must be himself! He could not doubt his own doubting. (Cathcart and Klein, 53)
As a result, Cathcart and Klein joke that perhaps Descartes should have said "dubito, ergo sum" -- although the reason why he did not is not explained by Cathcart and Klein, if we have followed the book thus far, we should be able to understand. To doubt ("dubito") is merely a subset of the general action of thinking ("cogito"). We might very well imagine that Descartes was thinking about how delicious his eggs had been at breakfast in flashes during his long sessions of epistemological skepticism -- or thinking about anything at all, in the way that human thought proceeds. The real point is that it is possible to doubt the evidence of the senses, but it is not possible to doubt the existence of an internal thought process which permits the action of "doubting." In other words, this is the only basic form of epistemological certainty, and Descartes would build the rest of his philosophy starting from that premise.
What is amusing is the way that Cathcart and Klein demonstrate the transition in epistemological approaches from the period of belief in the Middle Ages to the period…