Final answer:
Combining different shapes, lines, colors, and other art elements primarily achieves the principle of variety, providing interest and complexity in artwork.
Step-by-step explanation:
When different shapes, lines, colors, and other elements of art are combined to achieve a principle of design, the principle most typically achieved is variety. Variety in art introduces different forms, textures, colors, and values, creating interest and complexity within a piece. For instance, combining these different elements can provoke changes and raise awareness, contrasting with unity, which offers a sense of harmony and cohesiveness. However, too much variety without a sense of unity can result in a chaotic piece, and vice versa. Thus, achieving a balance between unity and variety is essential for a cohesive yet stimulating artwork.