As discussed above, profits are central to the goals of a firm and managerial decision making. Thus, to understand the theory of firm behavior properly, one must have a clear understanding of profits. While the term profit is very widely used, an economist's definition of profit differs from the one used by accountants (which is also usually used by the general public and the business community). Profit in accounting is defined as the excess of sales revenue over the explicit accounting costs of doing business. This surplus is available to the firm for various purposes.
An economist also defines profit as the difference between sales revenue and costs of doing business, but includes more items in figuring costs, rather than considering only explicit accounting costs. For example, inputs supplied by owners (including labor, capital, and space) are accounted for in determining costs in the definition used by an economist. These costs are sometimes referred to as implicit costs—their value is imputed based on a notion of opportunity costs widely used by economists. In other words, costs of inputs supplied by an owner are based on the values these inputs would have received in the next best alternative activity. For illustration, assume that the owner of the firm works for ten hours a day at his business. If the owner does not receive any salary, an accountant would not consider the owner's effort as a cost item. An economist would, however, value the owner's service to his firm at what his labor would have earned had he worked elsewhere. Thus, to compute the true profit, an economist will subtract the implicit costs from business profit; the resulting profit is often referred to as economic profit. It is this concept of profit that is used by economists to explain the behavior of a firm. The concept of economic profit essentially recognizes that owner-supplied inputs must also be paid for. Thus, the owner of a firm will not be in business in the long run until he recovers the implicit costs (also known as normal profit), in addition to recovering the explicit costs, of doing business.
As pointed out earlier, a given firm attempts to maximize profits. Other firms do the same. Ultimately, profits decline for all firms. If all firms are operating under a competitive market structure, in equilibrium, economic profits (the excess of accounting profits over implicit costs) would be equal to zero; accounting profits (equal to explicit costs), however would be positive. When a firm makes profits above the normal profits level, it is said to be reaping above-normal profits.
HOW A FIRM ARRIVES AT A PROFIT-MAXIMIZING POINT.
Let us assume throughout the discussion that a firm uses an economist's definition of profits. Assume that profit is the excess of sales revenue over cost (now assumed to be composed of both explicit and implicit costs). It can also be assumed, as discussed above, that the profit maximization is the firm's primary goal. Given this objective, important questions remain: How does the firm decide on the output level that maximizes its profits? Should the firm continue to produce at all if it is not profitable?
A manufacturing firm, motivated by profit maximization, calculates the total cost of producing any given output level. The total cost is made up of total fixed cost (due to the expenditure on fixed inputs) and total variable cost (due to the expenditure on variable inputs). Of course, the total fixed cost does not vary over the short run—only the total variable cost does. It is important for the firm to also calculate the cost per unit of output, called the average cost. In addition to the average cost, the firm calculates the marginal cost. The marginal cost at any level of output is the increase in the total cost due to an increase in production by one unit—essentially, the marginal cost is the additional cost of producing the last unit of output.
The average cost is made up of two components: the average fixed cost (the total fixed cost divided by the number of units of the output produced) and the average variable cost (the total variable cost divided by the number of units of the output produced). As the fixed costs remain fixed over the short run, the average fixed cost declines as the level of production increases. The average variable cost, on the other hand, first decreases and then increases; economists refer to this as the U-shaped nature of the average variable cost. The U-shape of the average variable cost curve is explained as follows. Given the fixed inputs, output of the relevant product increases more than proportionately as the levels of variable inputs used increase. This is caused by increased efficiency due to specialization and other reasons. As more and more variable inputs are used in conjunction with the given fixed inputs, however, efficiency gains reach a maximum—the decline in the average variable cost eventually comes to a halt. After this point, the average variable cost starts increasing as the level of production continues to increase, given the fixed inputs. First decreasing and then increasing average variable cost lead to the U-shape for the average variable cost. The combination of the declining average fixed cost (true for the entire range of production) and the U-shaped average variable cost results into an U-shaped behavior of the average total cost, often simply called the average cost.
The marginal cost also displays a U-shaped pattern—it first decreases and then increases. The logic for the shape of the marginal cost curve is similar to that for the average variable cost—both relate to variable costs. But while the marginal cost refers to the increase in total variable cost due to an increase in the production by one unit, the average variable cost refers to the average variable cost per unit of output produced. It is important to notice, without going into finer details, that the marginal cost curve intersects the average and the average variable cost curves at their minimum cost points.
In a graphic rendering of this concept there would be a horizontal line, in addition to the three cost curves. It is assumed that the firm can sell as many units as it wants at the given market price indicated by this horizontal line. Essentially, the horizontal line is the demand curve a perfectly competitive firm faces in the market—it can sell as many units of output as it deems profitable at price "p" per unit (p, for example, can be $10 per unit of the product under consideration). In other words, p is the firm's average revenue per unit of output. Since the firm receives p dollars for every successive unit it sells, p is also the marginal revenue for the firm.
A firm maximizes profits, in general, when its marginal revenue equals marginal cost. If the firm produces beyond this point of equality between the marginal revenue and marginal cost, the marginal cost will be higher than the marginal revenue. In other words, the addition to total production beyond the point where marginal revenue equals marginal cost, leads to lower, not higher, profits. While every firm's primary motive is to maximize profits, its output decision (consistent with the profit maximizing objective), depends on the structure of the market it is operating under. Before we discuss important market structures, we briefly examine another key economic concept, the theory of consumer behavior.
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