This paper aims to answer a complex question: Why is it so difficult to predict the infant's quality of attachment to its mother on the basis of maternal behaviors alone? Fonagy suggests that the attachment of a child to its mother represents the regaining of an intersubjective unity which had existed already in an earlier phase of development. The strength of such a unity, the mother's capacity to identify the mental state of her child, may be predictive of the quality of attachment of the infant. The paper discusses the implication of this model for the treatment of children whose attachment to their objects is disturbed.