Donald Norman's four classes of constraint


Norman suggests four classes of constraints that guide behavior, with the example of assembling a Lego motorcycle (Norman1988):

  • phsyical: "a large peg cannot fit into a small hole"
  • semantic: "the rider […] must sit facing forward"
  • cultural: the red light goes on the back of the motorcycle
  • logical: "all the pieces should be used, with no gaps in the final product"

Norman contrasts constraints, which restrict the possible behaviors to exclude invalid actions, with affordances, which indicate possible actions. Note that in Norman's terms, graphical elements are not affordances.

Norman provides a further example of logical constraints, in the form of "natural mappings":

Natural mappings work by providing logical constraints. There are no physical or cultural principles here; rather there is a logical relationship between the spatial or functional layout of components and the things that they affect or are affected by. If two switches control two lights, the left switch should work the left light, the right switch the right light. If the lights are mounted one way and the switches another, the natural mapping is destroyed. (Norman1988, 86)


[Norman1988] Norman, Donald (1988). The Psychology of Everyday Things. Basic Books.