however, a few alternations remain in what are now known as irregular verbs, such as je tiens, nous tenons; je dois, nous devons and je meurs, nous mourons. Some verbs had a more irregular alternation between different-length stems, with a longer, stressed stem alternating with a shorter, unstressed stem. That was a regular development stemming from the loss of unstressed intertonic vowels, which remained when they were stressed: j'aiu/aidier "help" < adiūtō, adiūtāre j'araison/araisnier "speak to" < adratiōnō, adratiōnāre je deraison/deraisnier "argue" < dēratiōnō, dēratiōnāre je desjun/disner "dine" < disiēiūnō, disiēiūnāre je manju/mangier "eat" < mandūcō, mandūcāre je parol/parler "speak" < *paraulō, *paraulāre < parabolō, parabolāre The alternation of je desjun, disner is particularly complicated; it appears that: Both stems have become full verbs in Modern French: déjeuner "to have lunch" and dîner "to dine". Furthermore, déjeuner does not derive directly from je desjun (< *disi(ēi)ūnō, with total loss of unstressed -ēi-). Instead, it comes from desjeüner, based on the alternative form je desjeün (< *disiē(i)ūnō, with loss of only -i-, likely influenced by jeûner "to fast" < jeüner < je jeün "I fast" < iē(i)ūnō: iē- is an initial rather than intertonic so the vowel -ē- does not disappear). Example of regular -er verb: durer (to last) Non-finite forms: Infinitive: durer Present participle: durant Past Participle: duré Auxiliary verb: avoir Example of regular -ir verb: fenir (to end) Non-finite forms: Infinitive: fenir Present participle: fenissant Past participle: feni(t) Auxiliary verb: avoir Example of regular -re verb: corre (to run) Non-finite forms: Infinitive: corre Present participle: corant Past participle: coru(t) Auxiliary verb: estre Examples of auxiliary verbs avoir (to have) Non-finite forms: Infinitive: avoir (earlier aveir) Present participle: aiant Past participle: eü(t) Auxiliary verb: avoir estre (to be) Non-finite forms: Infinitive: estre Present participle: estant Past participle: esté(t) Auxiliary verb: avoir Other parts of speech Adverbs, prepositions, conjunctions and interjections are generally invariable. Pronouns are usually declinable. See also History of French Anglo-Norman literature Arabic–Old French glossary Bartsch's law Explanatory notes References Citations General sources Grandgent, Charles Hall (1907). An introduction to Vulgar Latin. Boston: D.C. Heath & Co. Hall, Robert Anderson (October 1946). "Old French phonemes and orthography". Studies in Philology. Vol. 43, No. 4. 575–585. . Laborderie, Noëlle (2009). Précis de Phonétique Historique. Paris: Armand Colin. Rickard, Peter (1989). A history of the French language. London: Unwin Hyman. External links An Introduction to Old French by François Frédéric