Law of Diminishing Marginal Utility

The law of diminishing marginal utility states that the amount of satisfaction provided by the consumption of every additional unit of good decreases as we increase that good's consumption. Marginal utility is the change in the utility derived from consuming another unit of a good.

• The law of diminishing marginal utility refers to the quantity of satisfaction offered by each additional unit of good consumption decreases as we escalate the good’s utilization.
• Marginal utility refers to the change in the utility obtained from using another good unit.
• The assumptions of the law of diminishing marginal utility are rational consumers, continuous consumption, and standard size of units.
• The exceptions of diminishing marginal utility are addictions/hobbies, rare items, and unrealistic assumptions.

If we were to represent the law of diminishing marginal utility using a graph, it would look like the figure below. In this figure, the X-axis represents the number of units of a good consumed, and the Y-axis represents the marginal utility of that good. Notice that as we increase the number of units, the marginal utility of every additional unit falls. It keeps falling until it becomes zero and then further sinks to negative. After a certain point, consuming that good may cause dissatisfaction to the consumer.

Let us understand the concept first using some elementary examples of the law of diminishing marginal utility.

Example #1

Suppose a person is starving and has not eaten food all day. When he finally starts to eat, the first bite will give him a lot of satisfaction. As he keeps eating more and more food, his appetite will decrease and come to a point where he does not want to eat anymore.

Example #2

Suppose there is a manufacturer who has a huge demand for his products. To meet this demand, the manufacturer will employ more workforce. But eventually, there will come a point where hiring more workers does not benefit the organization. Instead, hiring more workers brings down the production per worker since the quantity demanded was being met by fewer workers. This example illustrates the law of diminishing marginal utility because hiring additional workers will not benefit the organization after a certain point.

• Rational Consumers - It requires consumers to behave rationally. They should make sound decisions at all times. The law assumes that consumers try to maximize utility subject to their incomes.
• Continuous Consumption - This assumption is fundamental for the law to hold. It means that the consumer continuously consumes every additional unit of the good. Therefore, there should not be intervals between the consumption of other units. For example, if a hungry person eats a pizza for lunch and then eats more pizza for dinner, the law is violated because the consumer is again hungry and derives increased utility from the second pizza than he would if he eats it right after lunch. So, intervals between the consumption of additional units violate the law.
• Standard Size of Units - The size of every unit should be common. If a person drinks half of a glass of water, drinking another half glass after it might not diminish the utility since he has not yet derived the total utility from consuming a full unit of the good. Reducing the size of units consumed is not consistent with the law of diminishing marginal utility.

• Addictions/Hobbies - This law does not hold in the case of addictions. The marginal utility of having an additional glass of alcohol does not decrease for an alcoholic. Similarly, in the case of hobbies, a person who likes to paint might not experience diminishing marginal utility in making a new painting.
• Rare Items - It also does not hold in the case of rare items. It is especially true for enthusiasts who chase such things and are passionate about them. For example, acquiring a limited-edition watch might give much more satisfaction to an enthusiast who likes collecting watches and already has many of them.
• Unrealistic Assumptions - Assumptions made by this law do not always hold. A consumer might make an irrational decision; there could be intervals between the consumption of units of a good, etc. Violating these assumptions might cause the law to not hold for a certain situation.

The law of diminishing marginal utility is widely studied in Economics. It helps us understand why consumers are less satisfied with every additional goods unit. The law is based on the ordinal utility theory and requires certain assumptions to hold. However, there are exceptions to the law as it might not have the truth in some cases.

This article is a guide to the Law of Diminishing Marginal Utility. We discussed the exceptions of the law of diminishing marginal utility with examples, assumptions, and graphical representation. You can learn more about it from the following articles: -

• Reflation
• Law of Diminishing Returns
• Formula of Marginal Revenue
• Average Cost vs Marginal Cost
• Formula of Marginal Propensity To Consume