"philosophical language". The third deals with "philosophical grammar" (universal grammar). The last part is the "alphabetical dictionary". It was compiled by William Lloyd. Wilkins' scheme Wilkin's "Real Character" is a constructed family of symbols, corresponding to a classification scheme developed by Wilkins and his colleagues. It was intended as a pasigraphy, in other words, to provide elementary building blocks from which could be constructed the universe's every possible thing and notion. The Real Character is not an orthography: i.e. it is not a written representation of spoken language. Instead, each symbol represents a concept directly, without (at least in the early parts of the Essay's presentation) there being any way of vocalizing it. Inspiration for this approach came in part from contemporary European accounts of the Chinese writing system, which were somewhat mistaken. Later in the Essay Wilkins introduces his "Philosophical Language", which assigns phonetic values to the Real Characters. For convenience, the following discussion blurs the distinction between Wilkins' Character and his Language. Concepts are divided into forty main Genera, each of which gives the first, two-letter syllable of the word; a Genus is divided into Differences, each of which adds another letter; and Differences are divided into Species, which add a fourth letter. For instance, Zi identifies the Genus of "beasts" (mammals); Zit gives the Difference of "rapacious beasts of the dog kind"; Zitα gives the Species of dogs. (Sometimes the first letter indicates a supercategory—e.g. Z always indicates an animal—but this does not always hold.) The resulting Character, and its vocalization, for a given concept thus captures, to some extent, the concept's semantics. The Essay also proposed ideas on weights and measure similar to those later found in the metric system. The botanical section of the essay was contributed by John Ray; Robert Morison's criticism of Ray's work began a prolonged dispute between the two men. Related efforts, discussions, and literary references The Essay has received a certain amount of academic and literary attention, usually casting it as brilliant but hopeless. One criticism (among many) is that "words expressing closely related ideas have almost the same form, differing perhaps by their last letter only...[I]t would be exceedingly difficult to remember all these minute distinctions, and confusion would arise, in rapid reading and particularly in conversation." (Umberto Eco notes that Wilkins himself made such a mistake in the Essay, using Gαde (barley) where apparently Gαpe (tulip) was meant.)