Variety

Variety is, in many ways, the opposite of unity. In some ways, variety is totally necessary in order to recognize distinct shapes and type (which also happen to be shapes). But it's more than that: variety breaks up a composition, relieving some of the monotony caused by extreme unity.

Unity and Variety to Achieve Content Flow

Extreme unity, as seen in the image below, actually inhibits eye movement through a composition. Breaking this unity with a little variety, demonstrating in the steps below, will help create better content flow and increase visual interest.

Extreme unity can feel dead and motionless

This creates a little movement beyond the grid

Some variation in thickness, though still very uniform throughout

More variety creates movement, but the edges feel harsh...

Edges continuity creates overall unity and helps eye movement...

Good combo of unity and variety; focal point creates hierarchy.

Variety in Type

Variety is an important concept found in type design as well. Within a typeface, a good variety of thick and thin, round and flat, or dark and light can give a single line of type a beautiful and pleasing rythym.

Garamond has a good contrast between thick and thin strokes

Didone faces like Modern No. 20 has super high contrast

Remove the contrast between elements and you remove much of the variety, leaving only the varied letterforms – which areobviously necessary for legibility and readability:

No serifs, no contrast between stroke widths.

Lastly, variety between typefaces in a single composition can also be a good thing...or it can be a complete disaster. A pairing of two typefaces can be quite complementary, and thus create a harmony between them:

But mix three or more typefaces and you've strayed way to far into variety territory and have thus broken unity: