Is anti-Israel sentiment a form of antisemitism? The question poses a political, legal and practical conundrum for universities like Columbia, Stanford and Harvard (where I teach), all of which currently have committees studying antisemitism. All these and other schools have been struggling with how to define and combat antisemitism while protecting academic freedom and freedom of speech. The best answer, it turns out, is that criticizing Israel or even opposing its existence isn’t inherently antisemitic as a matter of theory — but in practice, attacks on Israel can certainly become antisemitic when they cross over into bias against Jews as...