Quick question. And I promise it’s not a trick. Which direction is this line pointing?
If read left-to-right, the line has components of both upward and rightward direction. Read the other way, it takes on components of downward and leftward direction. Different cultures might interpret the slope as upward or downward depending on the direction of their written language.
What about this line?
Again—up, down, left, right—take your pick. For the purpose of communicating a direction, these lines clearly lack crucial information.
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In Gestalt’s Principles of Perception, the principle of Common Fate states that objects perceived to share a common fate are more related than objects that do not. This ability to relate things is fundamental to design.
Common Fate impacts our daily perception in subtle and surprising ways. In fact, the very notion you currently have that you are reading a specific sentence within a specific paragraph demonstrates the principle of Common Fate. The words in the previous paragraph ended at the previous line break, and the words of the current paragraph are doomed to their own fate right about now.
Much as typesetters and grammarians do with paragraphs and punctuation, UX and product designers exploit Gestalt’s insights in order to convey information effectively.
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Back to our lines.
Something very subtle and special happens when you bring together the two lines we contemplated above. Where one line is ambiguous, two lines must share a Common Fate. Missing information emerges. Two lines become one clear direction.
What I love most about this simple exercise with two lines is the emergent minimalism of Common Fate. Beyond the lines themselves, no special technique or superfluous decoration is required to build information. In this case, for communicating direction, alignment strategies alone do all of the work.
When I build design systems from which I intend full products to emerge, these humble lines always dance around in my mind, coming together to point in surprising directions, but always guiding me toward simplicity and clarity.