formal cause

In Aristotelian philosophy, the formal cause refers to the structure, essence, or pattern that defines a fully realized thing. It's what makes a thing what it is, essentially its form or blueprint. For example, the proportion of strings on a lyre that creates an octave is a formal cause. This concept is one of Aristotle's four types of causes, alongside material, efficient, and final causes. The formal cause explains a thing's nature and characteristic activities, and in living beings, it aligns with the final cause, as the mature realization of the form is the organism's ultimate goal.123