Old Occitan (Modern Occitan: occitan ancian, Catalan: occità antic), also called Old Provençal, was the earliest form of the Occitano-Romance languages, as attested in writings dating from the eighth through the fourteenth centuries. Old Occitan generally includes Early and Old Occitan. Middle Occitan is sometimes included in Old Occitan, sometimes in Modern Occitan. As the term occitanus appeared around the year 1300, Old Occitan is referred to as "Romance" (Occitan: romans) or "Provençal" (Occitan: proensals) in medieval texts.
The Old Catalan language diverged from Old Occitan between the eleventh and fourteenth centuries. Early texts in the Catalan dialect are the Homilies d'Organyà, Cançó de Santa Fe and the Greuges de Guitard Isarn. Catalan never underwent the shift from /u/ to /y/ or the shift from /o/ to /u/ (except in unstressed syllables in some dialects) so it had diverged phonologically before those changes affected Old Occitan.
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Some notable characteristics of Old Occitan:
The language had a two-case system (nominative and oblique), as in Old French, with the oblique derived from the Latinaccusative case. The declensional categories were also similar to those of Old French; for example, the Latin third-declension nouns with stress shift between the nominative and accusative were continued in Old Occitan only in nouns referring to people.
There were two distinct conditional tenses, a "first conditional" that was similar to the conditional tense in other Romance languages and a "second conditional" derived from the Latin pluperfect indicative tense. The second conditional is cognate with the literary pluperfect in Portuguese, the -ra imperfect subjunctive in Spanish, the second preterite of very early Old French (Sequence of Saint Eulalia), and probably the future perfect in modern Gascon.
From Bertran de Born's Ab joi mou lo vers e·l comens (ca. 1200, translated by James H. Donalson):
Bela Domna·l vostre cors gens E·lh vostre bel olh m'an conquis, E·l doutz esgartz e lo clars vis, E·l vostre bels essenhamens, Que, can be m'en pren esmansa, De beutat no·us trob egansa: La genser etz c'om posc'e·l mon chauzir, O no·i vei clar dels olhs ab que·us remir.
O pretty lady, all your grace
and eyes of beauty conquered me,
sweet glance and brightness of your face
and all your nature has to tell
so if I make an appraisal
I find no one like in beauty:
most pleasing to be found in all the world
or else the eyes I see you with have dimmed.
^Frank M. Chambers, An Introduction to Old Provençal Versification. Diane, 1985 ISBN 0-87169-167-1
^"The Early Occitan period is generally considered to extend from ca. 800 to 1000, Old Occitan from 1000 to 1350, and Middle Occitan from 1350 to 1550" in William W. Kibler, Medieval France: An Encyclopedia, Routledge, 1995, ISBN 0-8240-4444-4