The Cardinal Utility Approach, developed by economists like Alfred Marshall, assumes that utility (satisfaction) derived from consuming goods can be measured in absolute numbers or “utils.” It believes that consumers can quantify satisfaction, such as saying one apple gives 10 utils and two apples give 18 utils. The consumer aims to maximize total utility subject to income and prices. This approach uses the Law of Diminishing Marginal Utility and the Law of Equi-Marginal Utility to derive the demand curve. It forms the classical foundation of consumer theory, explaining how price changes affect demand.
Assumptions of Cardinal Utility:
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Measurability of Utility
The cardinal utility approach assumes that utility can be measured numerically, like weight or length. Consumers can assign specific numbers (utils) to the satisfaction derived from goods. For example, a person may say an apple gives 10 utils and an orange gives 5 utils. This measurability allows economists to compare and add utilities, making it possible to analyze total and marginal utility mathematically. Thus, the consumer’s satisfaction is treated as a quantifiable concept in decision-making.
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Constant Marginal Utility of Money
This assumption states that the marginal utility of money remains constant, regardless of the amount of money spent. Money serves as a stable measuring rod of utility, just like a ruler measures length. As the consumer buys more goods, the satisfaction from money used in purchasing remains unchanged. This constancy allows for accurate comparison between utility derived from goods and their prices. Without this assumption, measuring utility in monetary terms would become inconsistent and unreliable for analysis.
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Rational Consumer Behavior
The theory assumes that every consumer is rational and aims to maximize total satisfaction within a limited income. The consumer allocates expenditure among goods in a way that yields the greatest utility possible. Decisions are made logically, considering prices and preferences, without emotional or impulsive influences. Rational behavior ensures that consumers compare the utility obtained from each good with its cost and purchase accordingly. This assumption helps in predicting consumer choices scientifically and consistently.
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Independent Utilities
According to this assumption, the utility derived from one good is independent of the utility derived from another. For example, the satisfaction gained from consuming tea does not affect the satisfaction from consuming biscuits. Each good provides a separate and distinct utility. This independence simplifies the analysis of consumer behavior by allowing economists to study one good at a time. However, in real life, many goods are interdependent, making this assumption somewhat unrealistic.
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Diminishing Marginal Utility
The approach assumes that the marginal utility of a good decreases as more units of it are consumed. The first unit provides the highest satisfaction, and each successive unit gives less utility than the previous one. This principle, known as the Law of Diminishing Marginal Utility, explains why consumers are willing to pay less for additional units. It forms the foundation for the downward-sloping demand curve, showing the inverse relationship between price and quantity demanded.
Law of Diminishing Marginal Utility:
The Law of Diminishing Marginal Utility is the foundation of the cardinal approach. It states that as a consumer consumes more units of a commodity, the additional satisfaction (marginal utility) from each successive unit decreases. For example, the first apple gives high satisfaction, but the fifth apple gives much less. Since consumers derive less utility from each additional unit, they are willing to pay less for it. Thus, as price decreases, consumers buy more — forming the basis for the downward-sloping demand curve. This law establishes the psychological reason behind the negative slope of demand.
Law of Equi-Marginal Utility:
According to the Law of Equi-Marginal Utility, consumers allocate their income among various goods such that the marginal utility per rupee spent on each good is equal. Mathematically,
MUx / Px = MUy Py = MUz / Pz
If the price of one good (say, Px) falls, the ratio MUx / Px increases. To restore equilibrium, the consumer buys more of that good, reducing its marginal utility until equality is reestablished. This adjustment process shows that as price decreases, demand increases — resulting in a downward-sloping demand curve.
Derivation of Demand Curve (Cardinal Approach)
To derive the demand curve, consider a consumer purchasing one commodity at different prices while keeping income and other factors constant. At higher prices, the consumer buys fewer units because the marginal utility equals price at a lower quantity. As price decreases, the consumer buys more units until equilibrium (MU=PMU = P) is reached again. By plotting price on the vertical axis and quantity demanded on the horizontal axis, a downward-sloping demand curve is obtained. Each point on the curve represents the equilibrium between marginal utility and price at different levels of consumption.
Indifference Curves Map
This graph shows how a consumer chooses between two goods—X and Y—to maximize utility.
- Axes:
- Vertical axis = Quantity of Good Y
- Horizontal axis = Quantity of Good X
- Indifference Curves (IC₁ and IC₂):
- Each curve shows combinations of X and Y that give the same level of satisfaction.
- IC₂ lies above IC₁, indicating higher utility.
- Budget Line (AB):
- Represents all combinations of X and Y the consumer can afford.
- When the price of X changes, the slope of the budget line changes.
- Equilibrium Points (E₁ and E₂):
- Where the budget line is tangent to an indifference curve.
- These points show the optimal consumption bundle at different prices of X.
Demand Curve
This graph translates the consumer’s equilibrium choices into a demand curve for Good X.
- Axes:
- Vertical axis = Price of Good X
- Horizontal axis = Quantity Demanded of Good X
- Demand Curve (D):
- Downward-sloping, showing inverse relationship between price and quantity demanded.
- As price falls from P₁ to P₂, quantity demanded rises from Q₁ to Q₂.
- Points E₁ and E₂:
- Derived from the equilibrium points in the top graph.
- They show how changes in price affect the consumer’s demand.
Example of Cardinal Derivation:
Suppose a consumer’s marginal utility schedule for oranges is as follows:
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1st orange = 10 utils, 2nd = 8, 3rd = 6, 4th = 4, 5th = 2.
If the price per orange is ₹10, the consumer buys 1 orange (MU = P).
If the price falls to ₹8, he buys 2 oranges.
At ₹6, 3 oranges are bought, and so on.
Plotting these price-quantity points gives a downward-sloping demand curve. The curve illustrates that lower prices encourage higher consumption, reflecting diminishing marginal utility as more units are consumed.
Criticism of Cardinal Approach:
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Utility is Subjective and Immeasurable
The most fundamental criticism is that utility is a subjective, psychological phenomenon that cannot be objectively measured in cardinal (numerical) terms. Satisfaction is an internal feeling that varies from person to person; it lacks a standard unit of measurement like “utils.” One cannot conclusively say that the utility from a good is 10 for one person and 20 for another. Since it cannot be quantified, the core assumption of the cardinal approach is considered unrealistic and unscientific. This subjectivity makes interpersonal comparisons of utility, which are sometimes implied, fundamentally invalid.
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Constant Marginal Utility of Money is Unrealistic
The cardinal approach assumes the marginal utility of money remains constant to isolate the change in a good’s utility. Critics argue this is a highly unrealistic assumption. In reality, as a person’s stock of money changes, its marginal utility also changes—it diminishes as income increases. By ignoring this, the analysis becomes flawed. For example, when the price of a good falls, a consumer’s real income increases, which should change the marginal utility of money itself. The cardinal approach fails to account for this crucial income effect, leading to an incomplete analysis.
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It is an Introspective Method
The cardinal approach relies heavily on introspection, assuming that every consumer is consciously aware of the utils they derive from each unit of a commodity. In reality, consumers do not perform such mental calculations. They make choices based on preferences and budget constraints, not on numerical utility scores. This makes the theory behaviorally unrealistic. It describes a hypothetical, rational consumer rather than how actual people behave in markets. The approach is therefore seen as a theoretical construct with little empirical or practical validity for predicting real-world consumer behavior.
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Fails to Explain Related Goods (Substitutes and Complements)
The standard cardinal utility analysis, as presented by Marshall, primarily focuses on a single commodity. It does not adequately explain the consumption relationship between substitute and complementary goods. For instance, the utility derived from tea is intrinsically linked to the consumption and price of coffee (a substitute) or sugar (a complement). The cardinal approach struggles to analyze the consumer’s equilibrium when multiple related goods are considered simultaneously. This limitation makes it less versatile and comprehensive than the Ordinal Approach, which uses indifference curves to easily handle combinations of two or more goods.
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The Concept of Additive Utility is Flawed
The cardinal approach often assumes that the total utility from a basket of goods is the simple sum of the utilities derived from each individual good (U = Ux + Uy + …). This assumption of additive utility is problematic because the utility derived from one good is often interdependent with the consumption of another. For example, the utility from a car is enhanced by having petrol. Treating them as independent and additive oversimplifies consumer satisfaction, which is derived from the entire consumption bundle in a holistic and interconnected way, not from isolated items.