Which aspect of calligraphy is essential for creating an aesthetic appeal in letter forms?

Stroke contrast is a crucial element in calligraphy that significantly contributes to the overall aesthetic appeal of letter forms. This aspect refers to the variation in thickness and thinness of the strokes in letter shapes. By incorporating stroke contrast, calligraphers create visual interest and dynamics within the letters, making them more engaging and expressive.

When stroke contrast is mastered, it enhances legibility and adds a sense of rhythm and flow to the writing. This varying thickness can direct the viewer's attention and evoke emotional responses, which is vital in calligraphy that often seeks to convey a specific mood or feeling.

While letter spacing, pen angle, and ink quality are important aspects of calligraphy, none directly define the aesthetic appeal in the way that stroke contrast does. Letter spacing impacts legibility and readability, pen angle influences the style of the strokes, and ink quality affects the overall finish of the work, but it is the stroke contrast that primarily gives letters their beauty and distinctive character.