Economics is one of the oldest and most influential of intellectual disciplines. Practically all of the great thinkers, from Aristotle to Einstein, have tried their hand at it, and the great economists like Adam Smith, Thomas Malthus, David Ricardo, John Maynard Keynes and Milton Friedman rank among the most influential minds in our history.

There has long been something appealing for economists about the idea that the economy may behave with the same mathematical predictability of scientific laws such as Newton’s laws of motion. Newton’s laws reduce the whole complex, teeming, physical universe to three simple, reliable mathematical relationships. Is it possible to find similar relationships in the complex, changing world of markets?

The economy of India is expanding, thanks in large part to growth in industries like call centers and software development. The economies of many other nations are changing as well, while others, like that of the United States, have remained relatively stable for many years. In this section, you’ll learn that each nation’s economy depends on how that nation chooses to use its resources to satisfy people’s wants and needs.

The elasticity of demand is its responsiveness to changes in another factor, such as price. British economist Alfred Marshall is generally credited as the first economist to define the concept in 1890, but the German statistician Ernst Engel published a paper five years earlier, showing how changes in income alter the level of demand. The origins of the concept may be disputed, but its importance is not.

In the late 18th century Adam Smith wrote about the impact of competition on firms’ abilities to set prices and make profits above a “natural” level.

However, there was no formal analysis of the situation until British economist Alfred Marshall published Economic Principles in 1890. The ideas in Marshall’s model remain a key part of mainstream economic theory, although the theory has been criticized as not representing the true nature of competition.

The assumptions of Marshall’s model create certain consequences for firms in perfectly competitive industries. One of the most important of these is that firms have no power over the price that they can charge. This is because there are so many firms selling an identical product that if any one firm attempts to sell at a price higher than its competitors, it will sell nothing. This is virtually guaranteed because the consumer has perfect knowledge about the prices being asked by all firms. In this way the market price is determined by the collective interaction of all the firms and consumers, and each firm has to accept that one particular price is the price at which they can sell the product. They have to “take” the price, not make it.

Modern complex economies involve the interactions of large numbers of people and organizations. These economic agents fall into one of three categories: business, households, government, and the rest-of-the-world. Economists find it useful to think of these groupings as sectors of the economy. Let's look at each of these sectors in turn: