This pillar explores the evolution and mechanisms of mediums of exchange within market economies. We start with the barter system and progresses through the development of commodity money and fiat money, highlighting their roles in facilitating trade. The concept of market money is introduced as an alternative, reflecting money naturally emerging from market processes. We discuss the interest rate as a critical tool for regulating savings and investments, and time preference, which explains how people value present goods over future goods. The lecture also covers the price mechanism, the way prices coordinate economic activities, and economic calculations, essential for making informed production decisions. The pillar also examines the concepts of profits and losses as signals for business performance and capital accumulation as a form of charity and a driver of economic growth, and innovation, illustrating how they drive economic growth and efficiency within a market framework.

Keywords: Barter system, Commodity medium of exchange, Fiat Medium of exchange, Market Medium of Exchange, Price of Money, Interest Rate, Time Preference, Price Mechanism, Economic Calculations, Profits and Losses, Capital Accumulation, Innovation