 There are two works where al-Fārābī treats the notion of absolute certainty in detail. The first is his Book of Demonstration (Kitāb al-burhān) and the second is the Book on the Conditions of Certitude (Kitāb Šara’iṭ al-yaqīn). In both treatises al-Fārābī provides some conditions for absolute certainty. The second treatise contains an exhaustive account of these conditions, six in number: (1) to believe that something is in some way and not another, (2) to agree that this belief corresponds and is not opposed to the external existence of the thing, (3) to know the correspondence between the belief of the existence and the existence of the thing in reality, (4) to know that it is not possible for this correspondence to happen and there to be opposition, (5) to know that opposition between belief and reality cannot happen at any time, and (6) to know that all this is not accidental, but essential (al-Fārābī KY: 98). According to D. Black (2006: 16), these conditions can be understood as follows: