In 1890 alongside other realists (including Masaryk) he joined the Young Czechs. In the same year he returned to the Imperial Council. In the 1891 election he was successfully elected to the Vienna parliament for the Young Czechs. Here he delivered a formal declaration supporting self-determination and nationalism, but this declaration was not well supported. Historian Otto Urban judges Kaizl's declarations as being a manifestation of the Young Czech's overall views, despite the more radical views that had launched the Young Czech's to prominence. Due to Kaizl's efforts, the Young Czechs professed more moderate and rational arguments. Unlike Masaryk, Kaizl became a longstanding fixture within the Young Czech party. Kaizl played a critical role in becoming a moderating force against radicalism in the Young Czech party. In 1894 he helped prepare, alongside Karel Kramář, the Nymburská Resolution. This resolution called for "constructive opposition" against "false radicalism" found in the Young Czech party. In 1895 Masaryk and Kaizl had a disagreement due to Masaryk's criticism of liberalism and his support of the idea that common Czech national identity is rooted from the Czech Hussites; Kaizl instead advocated for the standard European liberal ideology and nationalism. Kaizl defined the concept of phasing politics, and said that the young Czechs are temperamentally connected to the liberalism and democratization of Austria-Hungary. Substantial disagreements between Masaryk, Kaizl, and other party members led to Masaryk's resignation and his formation of the Czech Progressive Party.