In 1979, a group of students in Tehran converted a foundational principle of the international system — the inviolability of diplomatic premises — into something that could be held, bargained over and ultimately compromised. When the hostages were released in January 1981, the US recovered its citizens. It never recovered the principle. The same mechanism is now at work in the Strait of Hormuz. Iran has not formally closed the waterway. It is changing its meaning.