‘I am not so vain to think’, wrote Locke in his Essay Concerning Human Understanding (1690) ‘that any one can pretend to attempt the perfect reforming the languages of the world, no not so much as that of his own country, without rendring himself ridiculous’. It seems highly probable that among the objects of Locke’s scorn were the universal or philosophical language planners, whose extravagant movement was approaching its unhappy end when he was formulating his masterpiece in the 1670s and ’80s. This article investigates what it was about their plans that made Locke jeer. While their schemes varied considerably, all were broadly con- cerned to map precisely and transparently the order of thoughts and things, often by means of ‘real characters’—written signs which can be understood by people who speak different languages. These projects were informed by a diverse and overlapping assortment of motivations and beliefs, such as irenicism, millenarianism, and Latitudinarianism, but two ambitions run prominently, if not completely, through the movement. The first looked to restore the Adamic harmony between language, mind, and world, whereby words would deliver knowledge of nature, and thereby read God’s other book in an act of piety. The second was that language should be universal. While the two overlap, in so far as the unity of the world vouchsafes semantic uniformity, and while commentators have often, and rightly, paid attention to the first of these ambitions, I am going to focus on the second. The goal to renovate a language which could be understood by all was nurtured in the shadow of Babel, and sparked by those injunctions of Francis Bacon which shaped the movement as a whole. Certain passages of The Advancement of Learning (1605), and especially of its Latin version, De dignitate et augmentis scientiarum (1623), exhorted philosophers to inquire further into ‘the notes of things and cogitations’. In particular, Bacon proposed that a ‘philosophical grammar’ might serve as ‘an antidote against the curse of the confusion of tongues’. In his Academiarum examen (1654), John Webster agreed that a ‘universal character’ would repair ‘the ruines of Babell’. The otherwise often distinctive voice of George Dalgarno chimed in with the promise in his first broadsheet, Character Universalis (1657), that by means of his ‘universal character’, ‘men of all nations may enjoy the benefit of conversing one with another’. And in his dedicatory letter to leading lights of the movement John Wilkins and Seth Ward, which prefaces his second broadsheet (Tables of the Universal Character, 1657), Dalgarno explained that what follows is intended ‘towards the releife of the confusion of languages’. Drawing on widespread, often tacit, suppositions, the planners premised their belief in the possibility of a shared language on the assumption that the entities which words represent are shared, that the meanings of words are the same for all.