Normal vs Inferior Goods

When a consumer’s income rises, they can afford more of everything — but that doesn’t mean they want more of everything. A normal good is one where consumption increases as income rises. An inferior good is one where consumption decreases as income rises, because the consumer switches to something better. Instant noodles, bus rides, and cheap beer are classic examples of inferior goods: as you get richer, you substitute toward restaurant meals, rideshares, and craft beer.

The distinction shows up visually in the Engel curve, which plots the quantity consumed of a good against the consumer’s income. For a normal good, the Engel curve slopes upward — more income, more consumption. For an inferior good, the Engel curve eventually bends backward — past some income threshold, higher income means less consumption of that good.

Walk income up step by step. The normal good keeps climbing — more is always better. The inferior good rises at first, then bends backward. That moment, around 5,000 dollars a month, is when the consumer can finally afford something better — and trades bus rides for cars and rideshares.

There’s also a finer distinction within normal goods. A luxury has an income elasticity greater than 1 — its budget share increases as income rises (e.g., designer clothing, overseas holidays); its Engel curve is convex (curves upward, consumption accelerating with income). A necessity has an income elasticity between 0 and 1 — consumption rises, but slower than income (e.g., bread, utilities); its Engel curve is concave (flattening out as income rises). Inferior goods have negative income elasticity.