This paper develops a framework for understanding inflation across the U.S. CPI basket by classifying prices according to how frequently they normally adjust and how exposed they are to international trade. Food and energy are analyzed separately rather than discarded. Flexible prices, food, and energy often respond first to both demand and supply shocks, while movements in sticky non-traded prices help assess whether initial pressures are spreading into persistent domestic price setting. Whether that propagation occurs depends on broader domestic and global conditions, including demand relative to supply, labour-market tightness, inflation expectations, exchange rates, supply chains, and policy settings. The pandemic illustrates this sequence: large movements first appeared in food, energy, and flexible prices, followed by stronger wage growth and broader increases in prices that normally adjust less frequently. Once inflation becomes embedded in sticky prices, strong inflationary pressures may require a more forceful monetary-policy response. The framework therefore organizes inflation analysis around shock arrival, propagation, persistence, and policy risk.