A friend of mine, not Jewish, kept asking me what was a reasonable definition of a Jew. At first I said such a definition was impossible, that every Jew would argue about it and no consensus would be reached. Still, he pressed on, when a Jew calls himself a Jew, what does he mean by it. Exasperated, I offered him this. It just might do the trick. Here's what I said:
A reasonable definition? You want a reasonable definition? How's about an unreasonable definition? Considering that most Jews would argue about any reasonable definition, the fact that they would get into an argument about it is a prerequisite to being Jewish. The definition of a Jew is this: if anybody offered a reasonable definition, a Jew would already take issue with it. Whoever would take issue with it is most certainly Jewish. They have the gene, they can't help themselves.
A Jew is also a person with Jewish parents, especially a Jewish mother, according to Jewish law. So if you have a Jewish mother and you consider yourself Jewish and if people ask you what's your race or religion, and you say Jewish, 99% of the time you are Jewish. You consider Jews your people, your race, your tribe, and you know a little about it.
The main things you know are that you are not Catholic or Protestant or Christian, you are not Muslim or Hindu. You are not a Native American or an African American. Your genes go back to Moses, about 3000 years ago. You think the Old Testament is more basic than the New Testament. You don't believe THE GREATEST STORY EVER TOLD, the virgin birth and the resurrection. Jesus was just another rabbi, who lived and died. You don't believe in the Divinity of Christ or Allah. You think God's name is Jehovah or Jahweh, not Jesus Christ or Allah.
You feel an affiliation with other Jews and you tend to have Jewish friends, friends with whom you can talk and joke about Jewish mothers and chicken soup and corned beef sandwiches and blintzes and latkes and borscht and knishes. It's all about food, what your soul food is. You feel at home in a Jewish delicatessen and a Chinese restaurant. You know that pizza is not your soul food and neither are chitlins or collard greens. You like to read and write and send letters to editors and discuss politics and religion endlessly.