The eucharistic argument is where Christian unity broke and stayed broken. The Fourth Lateran Council in 1215 used the word transubstantiation and Trent defined it: the substance of bread becomes the substance of Christ's body while every observable property of bread remains. The Orthodox affirm the change just as strongly, use the word metabole, and have generally refused to adopt the Aristotelian explanation, treating the how as none of anyone's business. Luther kept the real presence and rejected the philosophy; his 1529 meeting with Zwingli at Marburg agreed on fourteen articles and foundered on the fifteenth, which is why there are Lutherans and Reformed rather than one Protestantism. Zwingli's memorialism became the default in Baptist and most evangelical practice, where communion is monthly or quarterly rather than weekly. Who may receive follows directly: Catholic and Orthodox churches practise closed communion, and the resulting scene at an interchurch wedding, where half the family stays in the pew, is where the doctrine gets felt.