If it talks like a duck and walks like a duck, is it a duck? According to this first principle, yes! Similarity includes likeness in color, size, shape, or orientation. However, these defining characteristics can overlap. It’s important to recognize the hierarchy of the elements not to create competition for your most important content.

Similarity can create a sense of unity in your design through the use of similar fonts, colors, shapes, and such. It also helps the viewers differentiate the function of different elements. For example, coloring links or buttons can help lead a viewer to exploring.