A road stretching into the distance. Stairs climbing up a tall hill. A river winding through a city. Every day we experience similar scenes that lead our eyes through them, without even realizing it.
Continuation dictates how we interpret direction and movement through a composition. Our mind chooses the path of least resistance, perceiving lines as continuing along their established direction. In the examples below, our eye follows the less abrupt path, following the straight line or the curved path through the compositions on the left, more so than the jarring paths on the right. We tend to follow continuous, uninterrupted movement, following elements that are aligned in straight lines or curves. We perceive these aligned elements as related groupings more so than we do elements in lines and curves that are unaligned. This is the principle of continuation.