In search of balance: a review of Povinelli’s world without weight

Povinelli and colleagues ask whether chimpanzees can understand the concept of weight, answering with a resounding “no”. They justify their answer by appeal to over thirty previously unpublished experiments. I here evaluate in detail Povinelli’s arguments against his targets, questioning the assumption that such comparative questions will be resolved with an unequivocal “yes” or “no”.