It's an interesting question as to whether he really explains how a child goes from a concrete thinker to an abstract thinker, or how he goes from not having object permanence to understanding object permanence.

问题是,他是否真的解释了,儿童思维是如何从具体向抽象转变的,或是真的解释了,儿童的客体永存性概念是如何从无到有的

耶鲁公开课 - 心理学导论课程节选