Four studies are described in which children were asked to comprehend physical action passives such as Superman was held by Batman and mental verb passives such as Goofy was liked by Donald. Over a variety of comprehension methods, including questions in response to spoken sentences alone, or in choices of different pictures, children were found to be consistently poorer in comprehending the mental verb passives. Absolute competence could not be estimated securely because of variations in level of accuracy induced by different methods. But it appeared to be a reasonable interpretation that mental verb passives are understood very poorly at an absolute level by preschool children and many early grade school children, and are not understood as well as action verb passives until well into the grade school years. This is so despite the fact that both action and mental verb passives can be described uniformly at the level of the underlying grammatical relations, subject and object. Possibilities for explaining these limitations are discussed. It is concluded that it is not likely the children lack constructs such as subject, verb, and object. Rather, the limitations on the passive seem to arise from children's active construal of input as indicating semantic conditions on the applicability of the passive.