Theory of mind is a theory insofar as the mind is the only thing being directly observed.[1] The presumption that others have a mind is termed a theory of mind because each human can only intuit the existence of their own mind through introspection, and no one has direct access to the mind of another. It is typically assumed that others have minds analogous to one's own, and this assumption is based on the reciprocal, social interaction, as observed in joint attention,[6] the functional use of language,[7] and the understanding of others' emotions and actions.[8] Having theory of mind allows one to attribute thoughts, desires, and intentions to others, to predict or explain their actions, and to posit their intentions. As originally defined, it enables one to understand that mental states can be the cause of—and thus be used to explain and predict—the behavior of others.[1] Being able to attribute mental states to others and understanding them as causes of behavior implies, in part, that one must be able to conceive of the mind as a "generator of representations".[9][10] If a person does not have a complete theory of mind, it may be a sign of cognitive or developmental impairment.