Noun
formal cause (plural formal causes)
(philosophy, natural science) The design, pattern, or pure concept of a thing, which gives form or structure to its matter.
John Wesley stated in the 18th century, "In all cases, the Church is to be judged by the Scripture, not the Scripture by the Church." citation For this reason, sola scriptura is called the formal cause or principle of the Reformation. Source: Internet
A simple example of the formal cause is the mental image or idea that allows an artist, architect, or engineer to create his drawings. Source: Internet