什麼是供給與需求模型?

The Definition and Importance of the Supply and Demand Model
供給需求模型的定義與重要性

Forming the basis for introductory concepts of economics, the supply and demand model refers to the combination of buyers' preferences comprising the demand and the sellers' preferences comprising the supply, which together determine the Market prices and product quantities in any given market.
作爲經濟學入門概念的基礎，供給需求模型指的是：買方的偏好構成了需求，賣方的偏好構成了供給，而兩者結合起來決定了商品在任意市場形態中的價格和數量。

In a capitalistic society, prices are not determined by a central authority but rather are the result of buyers and sellers interacting in these markets.
在一個資本主義社會中，價格並不是由一箇中央權威制定的，而是這些市場中買方和賣方互動的結果。

Unlike a physical market, however, buyers and sellers don't have to all be in the same place, they just have to be looking to conduct the same economic transaction.
不過，這裏和有形的市場不同，買方和賣方並不需要同時處在一個地方，他們只需要期望進行同一場經濟交易即可。

It's important to keep in mind that prices and quantities are the outputs of the supply and demand model, not the inputs.
有一個很重要的點需要記住，那就是：價格與數量都是由供給需求模型決定的結果，而不是它的決定因素。

It's also important to keep in mind that the supply and demand model only applies to competitive markets — markets where there are many buyers and sellers all looking to buy and sell similar products.
還有一點很重要的是：供給需求模型僅適用於競爭性市場——也就是有很多買方和賣方想在此交易相似商品的地方。

Markets that don't satisfy these criteria have different models that apply to them instead.
那些不滿足這些要求的市場則適用不同的模型。

The Law of Supply and The Law of Demand
供給需求模型的法則

The supply and demand model can be broken into two parts: the law of demand and the law of supply.
供給需求模型可以被分解成兩個法則：需求法則和供給法則。

In the law of demand, the higher a supply's price, the lower the quantity of demand for that product becomes.
根據需求法則，一種產品的價格越高，對這種產品的需求量就越小。

The law itself states, "all else being equal, as the price of a product increases, quantity demanded falls; likewise, as the price of a product decreases, quantity demanded increases."
法則本身的說法是“在其他一切變量不變的前提下，當一件產品的價格升高，對其的需求量就會下降；相反，當一件產品的價格降低，對其的需求量就會增加。”

This correlates largely to the opportunity cost of buying more expensive items wherein the expectation is that if the buyer must give up consumption of something they value more to buy the more expensive product, they will likely want to buy it less.
這主要關係到買方買這種更貴產品時需要付出的機會成本，這其中的思路是：買方需要放棄購買某些他們覺得更有價值的東西來購買這件更貴的產品，所以他們可能會減少對它的購買量。

Similarly, the law of supply correlates to the quantities that will be sold at certain price points.
相似地，需求法則主要關係到在不同價位點會被售出的產品數量。

Essentially the converse of the law of demand, the supply model demonstrates that the higher the price, the higher the quantity supplied because of an increase in business revenue hinges upon more sales at higher prices.
供給模型從根本上來說是和需求模型相反的，它展現出的規律是：價格越高，供給量也越高，因爲當價格和銷量越高時，企業的盈利也就越高。

The relationship between supply in demand relies heavily on maintaining an equilibrium between the two, wherein there is never more or less supply than demand in a marketplace.
供給與需求的關係非常有效地導致兩者取得了一個平衡點，在這一點上，市場中的供給恰好等於需求。

Application in Modern Economics
（供給需求模型）在現代經濟學中的應用

To think of it in modern application, take the example of a new DVD being released for $15.
要想看它的現代版實例，我們來看一種定價爲15美元的DVD。

Because market analysis has shown that current consumers will not spend over that price for a movie, the company only releases 100 copies because the opportunity cost of production for suppliers is too high for the demand.
由於市場分析顯示目前的消費者不會付出比這更高的價格來看一部電影，所以公司決定把這個DVD發行100份；因爲，對於當前的需求量來說，供應方製造更多DVD的機會成本太高了。

However, if the demand rises, the price will also increase resulting in a higher quantity supply.
不過，當需求升高時，DVD的價格也會上升，然後就會導致供給量也上升。

Conversely, if 100 copies are released and the demand is only 50 DVDs, the price will fall to attempt to sell the remaining 50 copies that the market no longer demands.
相反，如果DVD發行了100份，而需求只有50份，價格就會下降以求售出那剩下的50份市場並不需要的DVD。

The concepts inherent in the supply and demand model further provide a backbone for modern economics discussions, especially as it applies to capitalist societies.
供給需求模型的核心概念給現代經濟學的各種討論奠定了基礎，對於資本主義社會尤其如此。

Without a fundamental understanding of this model, it is almost impossible to understand the complex world of economic theory.
如果不能理解這個基礎概念，那幾乎就不可能理解經濟學世界中的複雜理論。