Are there any sources in Judaism that a Jew who is an atheist is still Jewish, but a Jew who converts to another religion is not?

Question

Are there any sources for an idea in Judaism that somebody that is halacically Jewish and becomes atheist is still Jewish, but if they leave for another religion they are not?

I have heard of Jewish Atheists and not much objection to the idea of that being logically possible. Or, not a contradiction.

And I've heard of Jewish buddhists and not much objection to that idea, as being logically possible, and interestingly they say Buddhism isn't a religion.

Interestingly though, I have sometimes heard counter missionaries hit the roof when a christian missionary that is halachically Jewish, say that a person can be jewish and christian. I wonder if that's just them getting angry that a fellow Jew has converted to a religion of people that persecuted Jews so badly, historically or in the present eg christianity/islam, or if there is actually any halachic basis for the idea that eg if somebody converts to another religion then they are no longer considered Jewish?

Answer 1

The Talmud says:

אע"פ שחטא ישראל הוא -- Af’al pi shechata, Yisrael hu -- A Jew, even though he may sin, remains a Jew. [Sanhedrin 44a]

This means that no matter what a Jew does, he never ceases to be a Jew, and is still responsible for all the commandments. However, Israel's Law of Return, which is not the same as Jewish law, does not apply to a Jew who converted out of Judaism.

Answer 2

I recently ran into this article https://whatjewsbelieve.org/jews-for-jesus-messianic-jews-and-hebrew-christians-are-not-jews/

Here is a relevant portion of the article

" A rabbi in the later Middle Ages named the Hai Gaon, as quoted by Aderet in Responsa, VII #292, stated that a Jew who converted out of the faith was no longer a Jew. This view was shared by numerous rabbis, which can be seen in the Responsa literature of Simon ben Zemah of Duran, Samuel de Medina, Judah Berab, Jacob Berab, Moses ben Elias Kapsali and others in the Middle Ages.

It can also be seen more recently in the Responsa of the Satmar Rov in his Divrei Torah, Yoreh Deah #59, paragraph 5, as well as in the Responsa of Rabbi Moshe Feinstein, Even Haezer Volume 4 Number 53.

The very famous rabbi, Moses ben Maimon, called Maimonides (the Rambam), also wrote that if a Jew converted to Christianity, he or she was no longer a Jew. See Maimonides, Hilchot Mamrim Perek 3, Halacha 1-3, as well as in Maimonides’ Mishneh Torah, Avodat Kochavim 2:5.

Rabbi Moses Isserles demanded a formal conversion back to Judaism for those who had converted out, but then wanted to return. He demanded ritual immersion (mikveh) and repentance before a court of three (Beit Din). You will see this also in other Responsa literature: Radbaz, Responsa III, 415; Moses Isserles to Yoreh Deah 268.12; and Hoffman, Melamed Leho-il II, 84. "

And the article mentions that the Anusim are still Jewish because that was a forced conversion and involuntary, not like anything that would happen today.

I have to wonder where some of these sources would mean the same re atheism too. 'cos eg a bit later it uses aryeh kaplan a a source but his statement is more ambiguous. For example the article says

Furthermore, this is the attitude of many Orthodox rabbis today. In his book ‘The Real Messiah,’ Rabbi Aryeh Kaplan, writing for the Union of Orthodox Jewish Congregations of America and the Orthodox youth group ‘National Conference of Synagogue Youth,’ wrote (on page 21):

"This brings us back to our original question: What can a Jew lose by embracing Christianity? The answer is: Everything. Christianity negates the fundamentals of Jewish faith, and one who accepts it rejects the very essence of Judaism. Even if he continues to keep all of the rituals, it is the same as if he abandoned Judaism completely.

A Jew who accepts Christianity might want to call himself a ‘Jewish Christian,’ but he is no longer a Jew. He can no longer even be counted as part of a Jewish congregation."

So to Aryeh Kaplan it sounds like the pinnacle of no longer being a Jew, is no longer being counted as part of a jewish congregation..

Well, some would say atheists can't be counted for a Minyan, https://www.torahmusings.com/2019/01/including-non-religious-jews-in-a-minyan-and-its-discontents/ though i've never heard anybody say they are no longer Jewish. So I wonder if any of the sources that article gives would exclude atheists from being Jewish also. Or if some of the sources it mentions don't go as far as to say the person is no longer Jewish.

But anyow judging by that article there do seem to be sources that view conversion to another religion as a special case and the person is no longer considered Jewish.