"And this Reason has a Justification": Medieval Scientific Argument for the Custom against Eating Legumes on Passover

This article discusses a botanical-agricultural reason for the prohibition against eating legumes on Passover, one presented by Rabbeinu Manoah (Provence, thirteenth century). According to Rabbeinu Manoah, the basis of the prohibition is an ancient agricultural concept whereby through changes in climate and annual rainfall, wheat kernels become legumes. It seems that technical changes in agriculture in the Middle Ages affected the ban. The practice of using a three-field rotation of grains and legumes in European fields increased the mixture of aftergrowths of legumes from the previous years in the grain harvest of the present year. This phenomenon strengthened the ancient concept among contemporary agriculturists that grains had changed into legumes, when, in fact, the legumes were merely aftergrowths.