4. The historical development of both the powers and the privileges of Parliament indicates that they derive from the need to protect and promote the functioning of the legislature, originally in the face of threats or persecution of legislators by the monarch or the executive, and subsequently from interference from other sources such as the judiciary and civil society, which would undermine the functioning of the legislature. The rationale behind conferring special privileges and powers on the legislature can best be understood in the light of the doctrine of the separation of powers: that is that Parliament should regulate its affairs independantly of the other arms of government. Immunities or privileges generally fall within the following three categories.