Judicial review is a familiar illustration. The Constitution does not contain a sentence using those exact words to announce that the Supreme Court may refuse to enforce an unconstitutional federal statute. The practice rests on constitutional structure, the nature of written higher law, early argument, and precedent, especially Marbury v. Madison. The cabinet offers another example: Article II allows the president to seek written opinions from department heads, while practice developed those officers into a regular advisory body. Congressional committees and political-party leadership likewise became central without being specified in detail in the original text.

Informal does not mean imaginary or unimportant. A custom can guide officials for generations, and a judicial precedent can have enormous legal consequences. The word instead identifies how the development occurred: the text was not revised through Article V. That origin also marks a limit. Congress cannot pass an "informal amendment" that contradicts an explicit constitutional command, and a repeated custom does not automatically legalize conduct the Constitution forbids. Informal arrangements may also be easier to revise than formal text through later legislation, a new judicial precedent, executive change, party reform, or altered political expectations.

Use three questions to classify a scenario. Did the written constitutional language change? If yes, look for Article V. If no, which institution or practice produced the development-a court interpreting, Congress legislating, a president establishing practice, parties organizing, or officials following precedent? Finally, what could reverse it? A custom alterable through politics is different from an amendment that requires another constitutional change. Original ratification authorized the framework; formal amendment changes its text; informal development changes how the existing framework works. Keeping those levels separate is the chapter's final organizing skill.

Video lesson: The Constitution, the Articles, and Federalism: Crash Course US History #8