Deflation: causes

Deflation is the opposite of inflation. Therefore, under the usual contemporary definition of inflation, 'deflation' means a decrease in the general price level.[1] Alternatively, the term was used by the classical economists to refer to a decrease in the money supply; some economists, including many Austrian school economists, still use the word in this sense. The two meanings are closely related, since a decrease in the money supply is likely to cause a decrease in the price level.
Deflation is considered a problem in a modern economy because of the potential of a deflationary spiral and its association with the Great Depression, although not all episodes of deflation correspond to periods of poor economic growth historically.

Effects of deflation
In economic theory deflation is a general reduction in the level of prices, or of the prices of an entire kind of asset or commodity. Deflation should not be confused with temporarily falling prices; instead, it is a sustained fall in general prices. In the IS/LM model this is caused by a shift in the supply and demand curve for goods and interest, particularly a fall in the aggregate level of demand. That is, there is a fall in how much the whole economy is willing to buy, and the going price for goods. Because the price of goods is falling, consumers have an incentive to delay purchases and consumption until prices fall further, which in turn reduces overall economic activity - contributing to the deflationary spiral.
Since this idles capacity, investment also falls, leading to further reductions in aggregate demand. This is the deflationary spiral. The solution to falling aggregate demand is stimulus either from the central bank, by expanding the money supply, or by the fiscal authority to increase demand, and borrow at interest rates which are below those available to private entities.

In more recent economic thinking, deflation is related to risk, where the risk adjusted return of assets drops to negative, investors and buyers will hoard currency rather than invest it, even in the most solid of securities. This can produce the theoretical condition, much debated as to its practical possibility, of a liquidity trap. A central bank cannot, normally, charge negative interest for money, and even charging zero interest often produces less stimulative effect than slightly higher rates of interest. In a closed economy, this is because charging zero interest also means having zero return on government securities, or even negative return on short maturities. In an open economy it creates a carry trade and devalues the currency producing higher prices for imports without necessarily stimulating exports to a like degree.

In monetarist theory deflation is related to a sustained reduction in the velocity of money or number of transactions. This is attributed to a dramatic contraction of the money supply, perhaps in response to a falling exchange rate, or to adhere to a gold standard or other external monetary base requirement.

Deflation is generally regarded negatively, as it is a tax on borrowers and on holders of illiquid assets, which accrues to the benefit of savers and of holders of liquid assets and currency. In this sense it is the opposite of inflation (or in the extreme, hyperinflation), which is a tax on currency holders and lenders (savers) in favor of borrowers and short term consumption. In modern economies, deflation is caused by a collapse in demand (usually brought on by high interest rates), and is associated with recession and (more rarely) long term economic depressions.

In modern economies, as loan terms have grown in length and financing is integral to building and general business, the penalties associated with deflation have grown larger. Since deflation discourages investment and spending, because there is no reason to risk on future profits when the expectation of profits may be negative and the expectation of future prices is lower, it generally leads to, or is associated with a collapse in aggregate demand. Without the "hidden risk of inflation", it may become more prudent just to hold onto money, and not to spend or invest it.
Deflation is, however, the natural condition of hard currency economies when the rate of increase in the supply of money is not maintained at a rate commensurate to positive population (and general economic) growth. When this happens, the available amount of hard currency per person falls, in effect making money scarcer; and consequently, the purchasing power of each unit of currency increases. The late 19th century provides an example of sustained deflation combined with economic development under these conditions.

Deflation also occurs when improvements in production efficiency lower the overall price of goods. Improvements in production efficiency generally happen because economic producers of goods and services are motivated by a promise of increased profit margins, resulting from the production improvements that they make. Competition in the marketplace often prompts those producers to apply at least some portion of these cost savings into reducing the asking price for their goods. When this happens, consumers pay less for those goods; and consequently deflation has occurred, since purchasing power has increased.

While an increase in the purchasing power of one's money sounds beneficial, it can actually cause hardship when the majority of one's net worth is held in illiquid assets such as homes, land, and other forms of private property. It also amplifies the sting of debt, since-- after some period of significant deflation-- the payments one is making in the service of a debt represent a larger amount of purchasing power than they did when the debt was first incurred. Consequently, deflation can be thought of as a phantom amplification of a loan's interest rate.

This lesson about protracted deflationary cycles and their attendant hardships has been felt several times in modern history. During the 19th century, the Industrial Revolution brought about a huge increase in production efficiency, that happened to coincide with a relatively flat money-supply. These two deflationary catalysts led, simultaneously, not only to tremendous capital development, but also to tremendous deprivation for millions of people who were ill-equipped to deal with the dark side of deflation. Business owners-- on average, better educated in economic theory than their unfortunate cohorts (or just better able to withstand the economic stresses) -- recognized the deflation cycle as it unfolded, and positioned themselves to leverage its beneficial aspects.

Hard money advocates argue that if there were no "rigidities" in an economy, then deflation should be a welcome effect, as the lowering of prices would allow more of the economy's effort to be moved to other areas of activity, thus increasing the total output of the economy. However, while there have been periods of 'beneficial' deflation (especially in industry segments, such as computers), more often it has led to the more severe form with negative impact to large segments of the populace and economy.

Since deflationary periods favor those who hold currency over those who do not, they are often matched with periods of rising populist sentiment, as in the late 19th century, when populists in the United States wanted to move off hard money standards and back to a money standard based on the more inflationary (because more abundantly available) metal silver.

Most economists agree that the effects of modest long-term inflation are less damaging than deflation (which, even at best, is very hard to control). Deflation raises real wages which are both difficult and costly for management to lower. This frequently leads to layoffs and makes employers reluctant to hire new workers, increasing unemployment.

http://en.wikipedia.org/wiki/Deflation