  However, the circumstances under which it is appropriate to ascribe moral responsibility are not always clear. On the one hand the concept has varying meanings and debates continue on what sets moral responsibility apart from other kinds of responsibility (Hart 1968). The concept is intertwined and sometimes overlaps with notions of accountability, liability, blameworthiness, role-responsibility and causality. Opinions also differ on which conditions warrant the attribution of moral responsibility; whether it requires an agent with free will or not and whether humans are the only entities to which moral responsibility can be attributed (see the entry on  moral responsibility).