Islamic law and the social context of exchange in the medieval middle east

Islamic law purports to be unchanging and valid throughout the Islamic world. Nevertheless, a close examination of the medieval Islamic law of sate shows that the concept of local knowledge plays a considerable part in it On the one hand, the distinction between legitimate exchange and usury depends on the adequacy of the information available to the purchaser of goods or services; on the other hand, this stress on information leads to insistence that transactions must conform to the local custom of the merchants. Local custom thus comes in, as one might say, through a side door as a source of law, without being explicitly recognised as such.