In the essay, Wilkins defines his "real character", which is a new orthography for the English language that resembles shorthand, and his "philosophical language" which is based an early classification scheme or ontology (in what would later become the computer science meaning of the term).
Wilkins describes a large number of possible concepts as single words by first dividing all reality into forty different categories, each assigned to a different syllable, then sub-dividing these categories into sub-categories, and so on.
The resulting words thus encode some of the semantics of their meanings into their spelling. Such a-priori languages were inspired by accounts of how the Chinese writing system worked.
Jorge Luis Borges wrote a critique of Wilkins' philosophical language in his essay El idioma analítico de John Wilkins (The Analytical Language of John Wilkins).