How can someone be half Jewish?

Answer 1

Well nationality by definition is an association with a specific nation. Generally that is the nation you live in or grew up in so for example, I'm American because I live in the United States. Nationality can also be defined as a connection to a specific nation which your ancestors came from. You can consider yourself Jewish if you like, or you can consider yourself something else, it's whatever you choose. However, because Jerusalem is not a nation being Jewish is technically no longer considered a nationality it's a religion. In the end it's really your choice though

Answer 2

In the generally accepted definition of ethnicity, you can be, for example, half Irish and half German if one parent is Irish and one is German. People who apply that standard would say someone is half Jewish if they have a Jewish parent and a non-Jewish parent.

However, that ignores Jewish tradition. It's really impolite to tell someone that they are or are not a member of a minority group depending on the majority's idea of group membership.

Jewish tradition divides the world in two primary classes, Jews and non-Jews. There are no halfway cases. Jews are either converts or born to a Jewish mother. Non Jews did not have a Jewish mother and did not convert. (Some racists argue that Judaism is purely based on blood lines and they deny that converts are Jewish. Those racists ignore The Bible, where Ruth, an ancestor of King David, was a convert.)