The Jewish groups themselves reject characterization as sects. Sects are traditionally defined as religious subgroups that have broken off from the main body, and this separation usually becomes irreparable over time. Within Judaism, individuals and families often switch affiliation, and individuals are free to marry one another, although the major denominations disagree on who is a Jew. It is not unusual for clergy and Jewish educators trained in one of the liberal denominations to serve in another, and left with no choice, many small Jewish communities combine elements of several movements to achieve a viable level of membership.