The Latin phrase gradus ad Parnassum means "steps to Parnassus". It is sometimes shortened to gradus. The name Parnassus was used to denote the loftiest part of a mountain range in central Greece, a few miles north of Delphi, of which the two summits, in Classical times, were called Tithorea and Lycoreia. In Greek mythology, one of the peaks was sacred to Apollo and the nine Muses, the inspiring deities of the arts, and the other to Dionysus. The phrase has often been used to refer to various books of instruction, or guides, in which gradual progress in literature, language instruction, music, or the arts in general, is sought.
The first application of the phrase is to a kind of Latin or Greek dictionary, in which the quantities of the vowels are marked in the words, to help beginners to understand the principles of Latin verse composition, in relation to the values of the metrical feet. The first 'step' or lesson is contained in the title phrase itself, because 'gradus' being a fourth-declension noun (a step), with a short '-us' in the singular, becomes 'gradūs', with a lengthened '-ūs', in the plural (steps). The difference in meaning teaches one to observe the difference in vowel quantity between two forms which look the same but have different grammatical properties, and so to pronounce the title of the dictionary correctly. Then 'Parnassus' is a poetic figure alluding to the Muse (of poetry): and the second function of the Thesaurus is even so, to illustrate such figures. Therefore, the whole expression Gradus ad Parnassum is not just a title but an epitome of the work itself, combining declension, construction, scansion and figure.
The Gradus ad Parnassum made famous under the name of Jesuit Paul Aler (1656–1727), a schoolmaster, published in 1686, presented anew an earlier Thesaurus attributed to Pierre Joulet, sieur de Chastillon (1545–1621). This was not a general dictionary but a thesaurus of synonyms, epithets, verses and phrases in classical poetic usage. The work in Alers' form existed into the 19th century with the definitions as well as the entries written in Latin. Known to many generations of students throughout Europe, and passing through numerous editions, 19th century English-speaking schoolchildren knew the 1818 revision by Dr John Carey (1756–1826) simply as 'Carey's Gradus'. It was specially intended for the study and appreciation of Latin poetry of the classical period, and to aid students in the practice of verse composition. There is also a Latin gradus by C.D. Yonge (1850); English-Latin by AC Ainger and HG Wintle (1890); Latin-French by F.J.M. Noël (1810); Greek by Thomas Morell (1762, new ed. ed. by E. Maltby, Bishop of Durham, 1815); John Brasse (1828). Since the year 2000, the name Gradus ad Parnassum was incorporated as the name of a small music school in New Jersey, Gradus ad Parnassum Inc.
The large general dictionaries of Greek and Latin adopted this pattern of information. For example, the Liddell-Scott-Jones Greek-English Lexicon (1843) and its current derivatives give quantity information where it is crucial and where it is available; so do Charlton T. Lewis and Charles Short's A Latin Dictionary (1879) and its derivatives. The synonyms, epithets, poetical expressions and extracts became incorporated under the more important headings.
Charles Duke Yonge published A gradus ad Parnassum: For the use of Eton, Westminster, Harrow, and Charterhouse schools, King's college, London, and Marlborough college in 1850 a work that was still in print in 1902, by then titled …For the use of Eton, Westminster, Harrow, Charterhouse and Rugby schools, King's college, London, and Marlborough college and bound with A Dictionary of Epithets: Classified according to their English meaning.
Works entitled Gradus ad Parnassum include:
Doctor Gradus ad Parnassum is a satirical piano composition by Claude Debussy, from his suite Children's Corner, poking fun at Muzio Clementi's collection (or, as Myriam Chimènes states in the notes to the Arturo Benedetti Michelangeli version, at Czerny's collection).