We propose a mentalistic and nativist view of human early mental and social life and of the ontogeny of mindreading. We define the mental state of sharedness as the primitive, one-sided capability to take one's own mental states as mutually known to an interactant. We argue that this capability is an innate feature of the human mind, which the child uses to make a subjective sense of the world and of her actions. We argue that the child takes all of her mental states as shared with her caregivers. This allows her to interact with her caregivers in a mentalistic way from the very beginning and provides the grounds on which the later maturation of mindreading will build. As the latter process occurs, the child begins to understand the mental world in terms of differences between the mental states of different agents; subjectively, this also corresponds to the birth of privateness.