Diplomatic correspondence is correspondence between one state and another and is usually of a formal character. It follows several widely observed customs and style in composition, substance, presentation, and delivery and can generally be categorized into letters and notes. Letters Letters are correspondence between heads of state, typically used for the appointment and recall of ambassadors; for the announcement of the death of a sovereign or an accession to the throne; or for expressions of congratulations or condolence. Letters between two monarchs of equal rank will typically begin with the salutation "Sir My Brother" (or "Madame My Sister", in the case of a female monarch) and close with the valediction "Your Good Brother" (or Sister, in the case of a female monarch). In the case where one monarch is of inferior rank to the other (for instance, if the Grand Duke of Luxembourg were to correspond with the King of the United Kingdom), the inferior monarch will use the salutation "Sire" (or "Madame"), while the superior monarch may refer to the other as "Cousin" instead of "Brother". If either the sender or the recipient is the head-of-state of a republic, letters may begin with the salutation "My Great and Good Friend" and close with the valediction "Your Good Friend"; beneath the signature line will be inscribed "To Our Great and Good Friend [Name and Title of Recipient]". Letters of credence A letter of credence (lettres de créance) is the instrument by which a head of state appoints ("accredits") ambassadors to foreign countries. Also known as credentials, the letter closes with a phrase "asking that credit may be given to all that the ambassador may say in the name of his sovereign or government." The credentials are presented personally to the receiving country's head of state or viceroy in a formal ceremony. Letters of credence are worded carefully, as the sending or acceptance of a letter implies diplomatic recognition of the other government. Letters of credence date to the thirteenth century. Letters of recall A letter of recall is formal correspondence from one head-of-state notifying a second head-of-state that he or she is recalling his state's ambassador. Full powers In cases where an envoy is entrusted with unusually extensive tasks that would not be covered by an ordinary permanent legation (such as the negotiation of a special treaty or convention, or representation at a diplomatic congress), an envoy may be given