False. Consumer surplus provides an approximate measure of a change in consumer welfare even if the substitution effect is zero. The Slutsky equation provides a precise statement of the graphical analysis. The Slutsky equation decomposes the total effect of a price change into two components: the substitution effect and the income effect. The substitution effect measures the change in consumption due to the change in relative prices, while the income effect measures the change in consumption due to the change in purchasing power. If the substitution effect is zero, then the total effect of a price change is equal to the income effect. In this case, consumer surplus provides an exact measure of the change in consumer welfare, because it captures the entire change in consumer surplus due to the change in purchasing power. However, if the substitution effect is not zero, then the total effect of a price change is a combination of the substitution effect and the income effect. In this case, consumer surplus provides only an approximate measure of the change in consumer welfare, because it captures only the change in consumer surplus due to the change in relative prices, and not the change in consumer surplus due to the change in purchasing power. To illustrate this, consider the following diagram:         /|\         /|\          |           |          |           |          |           |          |           |          |           |          |           |          |           |          |           |          |           |          |           |          |           |          |           |          |           |          |           |          |___|          A           B Suppose the consumer faces an initial price of P1 and consumes Q1 units of the good. The consumer surplus is the area above the price line and below the demand curve, up to the quantity Q1. Now suppose the price decreases to P2, and the consumer consumes Q2 units of the good. The new consumer surplus is the area above the price line and below the demand curve, up to the quantity Q2. If the substitution effect is zero, then the consumer moves from point A to point C on the demand curve, where the new quantity demanded is Q2. In this case, the change in consumer surplus is exactly equal to the change in area between the price line and the demand curve, from Q1 to Q2. However, if the substitution effect is not zero, then the consumer moves from point A to point B on the demand curve, where the new quantity demanded is Q3. In this case, the change in consumer surplus is only approximately equal to the change in area between the price line and the demand curve, from Q1 to Q2, because it does not capture the change in consumer surplus due to the change in purchasing power. Therefore, consumer surplus provides an approximate measure of a change in consumer welfare even if the substitution effect is zero, and the Slutsky equation.