Rent is the reward for owning better land than the worst land still worth farming

When farmland grows scarce, cultivation spreads onto poorer soil. Ricardo showed that rent is simply the extra output the better land yields over that worst "marginal" plot still in use — landlords collect it for owning fertility, not for any effort. Rent doesn't cause high food prices; scarcity does, and rent is the result.

— David Ricardo, On the Principles of Political Economy and Taxation — Chapter II, 'On Rent', 1817
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