Work on philosophical languages was pioneered by Francis Lodwick (A Common Writing, 1647; The Groundwork or Foundation laid (or So Intended) for the Framing of a New Perfect Language and a Universal Common Writing, 1652), Sir Thomas Urquhart (Logopandecteision, 1652), George Dalgarno (Ars signorum, 1661), and John Wilkins (An Essay towards a Real Character, and a Philosophical Language, 1668). Those were systems of hierarchical classification that were intended to result in both spoken and written expression. In 1855, English writer George Edmonds modified Wilkins' system, leaving its taxonomy intact, but changing the grammar, orthography and pronunciation of the language in an effort to make it easier to speak and to read.[1]
Gottfried Leibniz created lingua generalis (or lingua universalis) in 1678, aiming to create a lexicon of characters upon which the user might perform calculations that would yield true propositions automatically; as a side effect he developed binary calculus.[2]
These projects aimed not only to reduce or model grammar, but also to arrange all human knowledge into "characters" or hierarchies. This idea ultimately led to the Encyclopédie, in the Age of Enlightenment. Under the entry Charactère, D'Alembert critically reviewed the projects of philosophical languages of the preceding century.
After the Encyclopédie, projects for a priori languages moved more and more to the fringe. However, from time to time, some authors continued to propose philosophical languages until the 20th century (for example, Ro, aUI) or even in the 21st century (Toki Pona).