Ideas are cheap. Durable ideas are rare. Friedman understood the difference. He didn't worry much about winning arguments with his contemporaries. He cared whether his work would still be useful decades later, still solving problems, still worth teaching to people who'd never heard his name. Time is brutal to most scholarship. The debates fade, the controversies lose their heat, and what looked brilliant in the moment gets quietly retired from the textbooks. But some ideas keep working. They bec