常識

1. Origins, structure, and basic meaning

• Structure: 常識 (じょうしき) is a noun for knowledge or behavioral standards broadly taken for granted in a society.
• Basic usage: 大声を控えるのは常識だ predicates public restraint as an expected norm, while 社会の常識も変わる says such norms can shift with time.

2. Common pitfalls and similar expressions

• Current norm and historical change
  • 常識だ asserts a norm in the society under discussion, whereas 常識も変わる shows it is not universal or immutable. Common sense is not identical to a legal provision.