Why is it necessary to establish the light-source direction before building the value structure in pencil shading?

Correct answer: To determine the logical placement of highlight, midtone, core shadow and cast shadow

The governing concept is a consistent light logic. The direction of the light source determines which planes face the light, where the highlight and midtone can appear, where the core shadow develops and in which direction the cast shadow falls. Establishing it first keeps every value connected to the same cause, so the form reads convincingly. Option A is correct; light direction does not select a pencil grade, alter paper texture or require a thicker contour.