W. Sanday,
The Criticism of the Fourth Gospel
“ But according to the Synoptics this Thursday would be Nisan 14, though on the Jewish reckoning (which counted the days from sunset to sunset) the Last Supper would fall on the beginning of Nisan 15. The Supper itself would be the regular passover, and the Crucifixion will have taken place after the passover. According to St. John we are expressly told that the Last Supper was held ‘before the passover’ (xiii. 1) , on what we should call the evening of Nisan 13, and the Jews the beginning of Nisan 14 ”
