Following the creation of Greater Romania at the end of World War I, Capidan followed his friend Sextil Pușcariu to the Transylvanian capital Cluj, where he spent nearly two decades, the most productive part of his career.
His research extended to reciprocal influences between Romanian and the surrounding Slavic languages, the Eastern Romance substratum and the Balkan sprachbund, as well as toponymy.
He was born into an Aromanian family in Prilep, a town that formed part of the Ottoman Empire's Manastir Vilayet and is now in North Macedonia.
After attending primary school in his native town, he followed his elder brother Pericle, a future painter, in emigrating to the Romanian Old Kingdom.
Slated to become a Romanian Orthodox priest, he studied at the central seminary in Bucharest, but decided he had a different vocation and left in order to pursue a teaching career.
[1][3] In 1907, he met and began a lifelong friendship with Sextil Pușcariu, who, after putting him through a three-month trial period in Czernowitz, invited the student to help with his Romanian-language dictionary project.
The following year, he became director of an institution he transformed into an exemplary place of learning, preparing not just economists but also students with an aptitude for science and literature.
He gathered dialectal, linguistic and folkloric material for future studies, undertook fieldwork and also used as subjects his students, Aromanians and Megleno-Romanians who came from throughout the Balkan peninsula.
Titled Réponse critique au Dictionnaire d'étymologie koutzovalaque de Constantin Nicolaïdi, it features both an argument based on science and a satirical flourish.
[5] During World War I, in common with the majority of Aromanian intellectuals in Macedonia, Capidan entered the Thessaloniki-headquartered Armée d'Orient as a volunteer.
After the war and the union of Transylvania with Romania, he was invited by Pușcariu to help place the new Superior Dacia University in Cluj on a solid foundation.
Pușcariu recalled how his colleague, together with Constantin Lacea, would sit daily in front of files for three or four hours, more than once ripping apart an article on which they had worked for a week and restarting in a more logical fashion.
[6] In 1937, Capidan was invited to the University of Bucharest, where he was made head of the comparative philology department heretofore led by the late Iuliu Valaori.
He published a critical and historical study of Hasdeu, placing him in the context of the development of Romanian linguistics and philology and championing his merits as an Indo-Europeanist.
He also published a series of etymological notes on the extinct language in the bulletin of the Academy's literary section, which he co-edited with his friend Dumitru Caracostea.
[14] Employing findings drawn from fieldwork, Capidan made observations about the bilingualism or even multilingualism of the sub-Danubian Romance peoples, and was the first Romanian scholar to study this phenomenon systematically.
He discussed the causes, evolution and implications of bilingualism, discovering evidence of linguistic interference, the first step toward the dialects' convergence and ultimate disappearance.
Initially, he believed that only a small part of the common features displayed by Romanian and Albanian were due to a shared native element, attributing the great majority of links to a reciprocal influence.
He used several of these to argue for the idea that certain Aromanians were native to Greece, basing the theory on their phonetic transformations found only in the Latin elements of Romanian.