>You're describing an "income effect." There's also a "substitution effect." The fundamental idea is that people will change their purchases in response to changing prices. If there's a sale on bread, then you might pick up an extra loaf (substitution effect). But if you were a peasant mainly eating bread, then you might actually purchase less bread and more cheese (income effect).

Maybe you'll substitute cheese for bread, but you're not going to substitute a TV and some extra pairs of jeans for your electricity and gas.