Apostasy and Practiced Halakhah: From the Talmudic Lexicon to Medieval and Modern Decision-Making. Continuing to explore our question of "What is a Jew?" through the medieval sources, we will focus on two case studies (i) Marriage, and (ii) the procedure for reconverting apostates if and when they return to Judaism. Can Jews and apostates contract valid Jewish marriage? If apostates return to Jewish practice and community must they reconvert?