Jewish atheism refers to the atheism of people who are ethnically and (at least to some extent) culturally Jewish. Contrary to popular belief, the term "Jewish atheism" is not a contradiction because Jewish identity encompasses not only religious components, but also ethnic and cultural ones. Jewish law's emphasis on descent through the mother means that even religiously conservative Orthodox Jewish authorities would accept an atheist born to a Jewish mother as fully Jewish. Jewish secularism, which describes Jews who do not explicitly reject the existence of God but also do not believe it is an important part of their Jewishness, has a long tradition in the United States. A 2013 study conducted by the Pew Research Center found that 62% of self-described American Jews say being Jewish is mainly a matter of ancestry and culture, while just 15% say it is mainly a matter of religion. Even among Jews by religion, 55% say being Jewish is mainly a matter of ancestry and culture, while 66% say it is not necessary to believe in God to be Jewish. Organized Jewish life There has been a phenomenon of atheistic and secular Jewish organizations, mostly in the past century, from the Jewish socialist Bund in early twentieth-century Poland to the modern Congress of Secular Jewish Organizations and the Society for Humanistic Judaism in the United States. Many Jewish atheists feel comfortable within any of the three major non-Orthodox Jewish denominations (Reform, Conservative, and Reconstructionist). This presents less of a contradiction than might first seem apparent, given Judaism's emphasis on practice over belief, with even mainstream guides to Judaism suggesting that belief in God is not a necessary prerequisite to Jewish observance. However, Orthodox Judaism regards the acceptance of the "Yoke of Heaven" (the sovereignty of the God of Israel in the world and the divine origin of the Torah) as a fundamental obligation for Jews, and the Reform movement has rejected efforts at affiliation by atheistic temples despite many Reform Jews being atheist/agnostic. Nevertheless, the presence of atheists in many denominations of modern Judaism from Secular Humanistic Judaism to Conservative Judaism has been noted. Jewish theology Nineteenth-century and early twentieth-century Reform Judaism in the US, which had become the dominant form of Judaism there by the 1880s, was profoundly shaped by its engagement with high profile skeptics and atheists such as Robert Ingersoll and Felix Adler. These included the writings of rabbis such