 He vacated his chair of Basque studies in 1920 to immerse himself fully with the work of the Euskaltzaindia, pushing initiatives to codify and promote the Basque language, against considerable opposition from official quarters and the Arana camp.His main study on Basque morphology, 'Morfología Vasca' and the collection of Basque folks songs, "Cancionero Popular Vasco", fall into this period.He also developed the famous "Erizkizundi Irukoitza" ('Triple Questionnaire'), a substantial tool to elicit information on vocabulary, morphology and pronunciation of Basque from informants.