There can be no question that Israel has a right to defend itself. But there are legitimate questions about how it does so. Its many friends and allies have insisted that it must comply with the stipulations of international law, and Israel has said it intends to do so. Its generals argue that to minimise civilian casualties it has accepted extra risks to its own soldiers. But above it all hangs the key question: is Israel’s war aim – the elimination of Hamas – achievable? The principles of the Just War tradition are at the bedrock of international law and are the moral basis for the legal requirements that Israel has to comply with. And one of the primary questions that Just War theory asks each side in any armed conflict is, Do you have a reasonable prospect of success?