The law of demand states that price and quantity demanded move in opposite directions, all else equal (ceteris paribus), producing a downward-sloping demand curve. A change in price causes a movement along the demand curve (change in quantity demanded). A change in a non-price determinant shifts the entire curve left or right (change in demand). The INSECT acronym covers the main demand shifters: Income, Number of consumers, Substitutes, Expectations of future price, Complementary goods, and Tastes and preferences. Normal goods see demand rise with income; inferior goods see demand fall with income.
- Law of demand: As price rises, quantity demanded falls; as price falls, quantity demanded rises, ceteris paribus.
- Movement along vs. shift: A price change moves you along the existing demand curve; a change in a non-price determinant shifts the whole curve.
- INSECT acronym: Income, Number of consumers, Substitutes, Expectations, Complementary goods, Tastes: the six non-price determinants that shift demand.
- Normal vs. inferior goods: Demand for normal goods rises when income rises; demand for inferior goods falls when income rises.
If consumer incomes rise and the good is a normal good, does the demand curve shift left or right? What happens to equilibrium price?
| Event | Effect on demand curve | Direction of shift |
|---|
| Income rises (normal good) | Demand increases | Rightward |
| Income rises (inferior good) | Demand decreases | Leftward |
| Price of substitute rises | Demand increases | Rightward |
| Price of complement rises | Demand decreases | Leftward |
| Consumers expect higher future prices | Demand increases now | Rightward |