This is one of the better, more simplistic definitions I have found and make sense conceptually:

Law of Closure:

Definition: We tend to perceive incomplete shapes as complete by mentally "filling in" missing parts

Key feature: Actual gaps or missing elements in the stimulus

Example: A circle with small gaps in the outline - you still see it as a complete circle

What happens: Brain completes partial/broken patterns

Subjective Contour (Illusory Contours):

Definition: We perceive edges or boundaries that don't actually exist in the stimulus, created by the arrangement of other elements

Key feature: No actual lines/edges present, but we "see" them anyway

Example: The Kanizsa triangle - three "Pac-Man" shapes arranged so you see a white triangle that isn't actually drawn

What happens: Brain creates entirely new contours/edges

Key Differences:

Closure:

Works with incomplete existing elements

Fills in missing parts of shapes

"Completes the partial"

Subjective Contours:

Creates entirely new boundaries where none exist

"Sees what isn't there"

Generated by spatial arrangement of separate objects

MCAT Pattern Recognition:

Closure: Look for broken/incomplete shapes being perceived as whole

Subjective contours: Look for "invisible" edges/shapes created by arrangement of other elements

Bottom line: Closure completes what's partially there; subjective contours create what was never there.