This is a collection of five essay, some comprising material "left over" from The Search for the Perfect Language, on an eclectic range of subjects. I read it because someone somewhere (I forgot to note who or where) suggested that it provided a good test of whether you would enjoy reading that longer work. I failed the test, and so now probably won't be reading further. I'm not sure if the fault lies in me, the author, or the translator, but I found the essays mostly a ramble through confusing landscape of ideas, phrased in unnecessarily esoteric language.
The first essay, "The Force of Falsity", gives examples of how false ideas can have nevertheless have profound effects. The first example he gives is the belief that Columbus' contemporaries believed the earth is flat (they did not), a false idea used in the 19th century to help attack the church. He then moves on to other examples, including the Donation of Constantine (which I'd never even heard of until wikipedia came to my aid), the legend of Prester John (which I'd heard of by name, but didn't know any more, having it somehow vaguely mangled with the Arthurian tales in the back of my brain, until wikipedia came to my aid, again). The final one is tracing from the Rosicrucian spoof, via some 17th century satirical and political novels, to the full blown sheer nastiness of the Protocols of the Elders of Zion, a false idea (read, evil propaganda) that had profound tragic effects.
Eco is contrasting this "The Force of Falsity" with the "Force of Truth" notion. But, of course, these ideas aren't known, or admitted, to be false by those under their influence. It's more that ideas can be powerful motivators, particularly when they provide confirmation, or at least a convenient excuse, for doing what you wanted to do anyway. I liked his recounting Popper's idea of why conspiracy theories are popular: once there are no more superbeings to take the rap, who are you going to blame for all the bad stuff?
The next essay, "Languages in Paradise", is a history of attempts to recreate a perfect language, either the one Adam spoke in Eden, or a suitable alternative, focussing on Dante's work in this area. It appears to be proposing a new hypothesis in this area, but I found it hard to tell, not being a mediaeval scholar. (I have been informed by a colleague who is a mediaeval scholar that you need to be one to fully appreciate even The Name of the Rose, so it shouldn't be surprising that an academic non-fiction piece requires even more background -- but I was hoping for a little more accessibility in something marketed as a "popular" book.) It is also hard to tell whether Eco actually believes in Adam as an historical character, or is engaging in a rather ponderous joke:
"From Marco Polo to Leibniz" is an essay on cultural misunderstandings, particularly how people interpret what they see in terms of what they expect. Hence Marco Polo's report of a unicorn, which was actually a rhinoceros, and Leibniz' misinterpretation of the I Ching in terms of his calculus of thought.
"The Language of the Austral Land" is a report of various artificial languages, and a discussion of the role of Chinese in the search for a perfect language. This is, to me, the most interesting essay in the book, and had some material on artificial languages not included in In the Land of Invented Languages
The final essay is "The Linguistics of Joseph de Maistre", where Eco dissects the work of an early linguist. Again, there is interesting stuff here, but I'm not sure I gained a full understanding of whatever Eco's point is, due to the overly-elliptical style, and presumption of rather more background knowledge of esoterica than I actually have.
If you have such background, you may get more out of this book than I did. I read to learn new things. I delight in the wit and erudition of the author when they help me understand, not when they obscure their points (and particularly not when they appear to be delighting in their own wit and erudition). So, for me, on to other authors.