For a normal good in consumer theory, how does the demand for that good typically change when the consumer's income increases?

Introduction / Context:
In microeconomics, goods are often classified as normal or inferior based on how their demand responds to changes in consumer income. This is a fundamental concept when analysing income effects and drawing Engel curves. A normal good is one that consumers buy more of as their income rises. This question asks for the correct description of how demand for a normal good changes with an increase in the consumer's income.

Given Data / Assumptions:

• The good in question is explicitly stated to be a normal good.
• The consumer's income is assumed to increase.
• Other factors such as prices of goods and tastes are assumed to remain constant (ceteris paribus).
• We are asked about the direction of change in demand, not the exact magnitude.

Concept / Approach:
For a normal good, the income effect is positive. This means that when income rises, the quantity demanded of the good also rises, holding other things equal. This relationship arises because consumers now have more purchasing power and can afford a higher quantity or better quality of the good. In contrast, an inferior good has a negative income effect: when income increases, demand for that good decreases, as consumers switch to higher quality alternatives. The key idea here is the sign of the relationship between income and demand. With a normal good, that sign is positive.

Step-by-Step Solution:
Step 1: Identify that the good mentioned in the question is normal, which implies a positive income effect.Step 2: Consider an increase in the consumer's income, while keeping prices and preferences constant.Step 3: For a normal good, higher income allows the consumer to purchase more of the good, reflecting higher demand.Step 4: This means that the demand curve for the normal good shifts to the right as income rises.Step 5: Therefore, the change in demand associated with an income increase is an increase in quantity demanded at each price level.Step 6: Among the options, "Increase" correctly describes this outcome.

Verification / Alternative check:
Think of common examples of normal goods, such as better quality food, clothing, or electronic devices. When people's incomes rise, they generally buy more of these goods or upgrade to more expensive brands. Demand does not stay constant, nor does it automatically double in a fixed proportion, but it clearly shows an upward tendency. This everyday observation, supported by empirical data and theoretical models, confirms that demand for normal goods rises with income, consistent with the definition.

Why Other Options Are Wrong:
"Decrease" is wrong because it reflects the behaviour of inferior goods, not normal goods. "Remain constant" is incorrect because normal goods are defined specifically by the fact that their demand changes with income, rather than staying unchanged. "Double" is also incorrect because while demand may increase, there is no requirement that it doubles; the relationship is positive but not necessarily a fixed multiple. Thus, only "Increase" is both precise and consistent with the definition of a normal good.

Common Pitfalls:
Students sometimes confuse normal and inferior goods due to the word "normal" sounding casual. It is important to remember that a normal good has a positive income elasticity of demand, while an inferior good has a negative income elasticity. Another pitfall is assuming that the increase has to be proportional or very large; in reality, any positive relation, even a small one, qualifies the good as normal. Focusing on the sign of the income effect rather than its size helps reduce confusion.

Final Answer:
For a normal good, the demand increases when the consumer's income increases.