What is law of equi- marginal utility? Also explain this law with the help of a table.

Law of Equi-marginal Utility

The Law of Equi-marginal Utility is another fundamental principle of Economics. This law is also known as the Law of substitution or the Law of Maximum Satisfaction. We know that human wants are unlimited whereas the means to satisfy these wants are strictly limited. It, therefore, becomes necessary to pick up the most urgent wants that can be satisfied with the money that a consumer has. Of the things that he decides to buy, he must buy just the right quantity. Every prudent consumer will try to make the best use of the money at his disposal and derive maximum satisfaction.

Assumptions of Law of Equi-Marginal Utility

• Units of goods are homogenous.
• No time gap between the consumption of the different units.
• Tastes, fashion, preferences, and priorities remain unchanged.
• Consumer aims at maximum satisfaction.
• Consumer’s income is fixed and limited.

Explanation of the Law

In order to get maximum satisfaction out of the funds we have, we carefully weigh the satisfaction obtained from each rupee ‘had we spend If we find that a rupee spent in one direction has greater utility than in another, we shall go on spending money on the former commodity, till the satisfaction derived from the last rupee spent in the two cases is equal.

In other words, we substitute some units of the commodity of greater utility for some units of the commodity of less utility. The result of this substitution will be that the marginal utility of the former will fall and that of the latter will rise, till the two marginal utilities are equalized. That is why the law is also called the Law of Substitution or the Law of Equi-marginal Utility.

Suppose apples and oranges are the two commodities to be purchased. Suppose further that we have got seven rupees to spend. Let us spend three rupees on oranges and four rupees on apples. What is the result? The utility of the 3rd unit of oranges is 6 and that of the 4th unit of apples is 2.
As the marginal utility of oranges is higher, we should buy more oranges and fewer apples. Let us substitute one orange for one apple so that we buy four oranges and three apples.

Now the marginal utility of both oranges and apples is the same, i.e., 4. This arrangement yields maximum satisfaction. The total utility of 4 oranges would be 10 + 8 + 6 + 4 = 28 and of three apples 8 + 6 + 4= 18 which gives us a total utility of 46. The satisfaction given by 4 oranges and 3 apples at one rupee each is greater than could be obtained by any other combination of apples and oranges. In no other case does this utility amount to 46. We may take some other combinations and see.

We thus come to the conclusion that we obtain maximum satisfaction when we equalize marginal utilities by substituting some units of the more useful for the less useful commodity. We can illustrate this principle with the help of a diagram.

Diagrammatic Representation

In the two figures given below, OX and OY are the two axes. On X-axis OX are represented the units of money and on the Y-axis marginal utilities. Suppose a person has 7 rupees to spend on apples and oranges whose diminishing marginal utilities are shown by the two curves AP and OR respectively.

The consumer will gain maximum satisfaction if he spends OM money (3 rupees) on apples and OM’ money (4 rupees) on oranges because in this situation the marginal utilities of the two are equal (PM = P’M’). Any other combination will give less total satisfaction.

Let the purchase spend MN money (one rupee) more on apples and the same amount of money, N’M'( = MN) less on oranges. The diagram shows a loss of utility represented by the shaded area LN’M’P’ and a gain of PMNE utility. As MN = N’M’ and PM=P’M’, it is proved that the area LN’M’P’ (loss of utility from reduced consumption of oranges) is bigger than PMNE (gain of utility from increased consumption of apples). Hence the total utility of this new combination is

We then conclude that no other combination of apples and oranges gives as great a satisfaction to the consumer as when PM = P’M’, i.e., where the marginal utilities of apples and oranges purchased are equal, with given amour, of money at our disposal.

Limitations of the Law of Equimarginal Utility

Like other economic laws, the law of Equi-marginal utility too has certain limitations or exceptions. The following are the main exception.

1. Ignorance

If the consumer is ignorant or blindly follows custom or fashion, he will make the wrong use of money. On account of his ignorance, he may not know where the utility is greater and where less. Thus, ignorance may prevent him from making rational use of money. Hence, his satisfaction may not be the maximum, because the marginal utilities from his expenditure cannot be equalized due to ignorance.

2. Inefficient Organisation

In the same manner, an incompetent organizer of business will fail to achieve the best results from the units of land, labor and capital that he employs. This is so because he may not be able to divert expenditure to more profitable channels from the less profitable ones.

3. Unlimited Resources

The law has obviously no place where these resources are unlimited, as for example, is the case with the free gifts of nature. In such cases, there is no need of diverting expenditure from one direction to another.

4. Hold of Custom and Fashion

A consumer may be in the strong clutches of custom or is inclined to be a slave of fashion. In that case, he will not be able to derive maximum satisfaction out of his expenditure, because he cannot give up the consumption of such commodities. This is especially true of the conventional necessaries like a dress or when a man is addicted to some intoxicant.

5. Frequent Changes in Prices

Frequent changes in prices of different goods render the observance of the law very difficult. The consumer may not be able to make the necessary adjustments in his expenditure in a constantly changing price situation.