So, whatever the Lawgiver has ruled upon and Himself defined must be referred back to its legal definition; whatever He has ruled upon but left undefined, content with the clarity of its linguistic sense, must be referred back to the language; and whatever has received no definition in either the Sharīʿa or the language is referred to the people’s prevailing practice and custom. The Lawgiver may even state explicitly that such matters be determined by custom, as in the commands to “enjoin what is customary (al-maʿrūf)” and to “live with them in a manner that is customary,” and the like. Commit these foundations to memory, for the jurist is compelled to rely on them in every aspect of his legal deliberations.