Chapter 4 focuses on the use of constraints in design. Designers can guide user behavior by combining “knowledge in the world,” such as cultural, logical, and semantic constraints, with physical constraints or explicit design cues, all of which help users determine how to use products.

Four Kinds of Constrains: Physical, Cultural, Semantic, and Logical

This section describes four types of constraints, all of which limit possible operations. The first, physical constraints, are most effective when they are easy to see and interpret. Norman uses the example of batteries to explain this point. Cylindrical batteries lack sufficient constraints because they fit inside battery compartments in two directions (one correct, the other incorrect). They also lack signifiers, making it difficult to determine the proper orientation. Norman recommends designing batteries that make orientation irrelevant, inventing contacts that allow batteries to be inserted in either direction, or creating batteries that only fit into compartments in one way. He argues that the current design persists because of a “legacy problem”—namely, that too many manufacturers have adopted it and made it the standard.

Culture presents constraints by limiting possible actions in certain social settings. Violating cultural norms, such as facing the rear of an elevator, makes people uncomfortable.