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.
作为经济学入门概念的基础，供给需求模型指的是：买方的偏好构成了需求，卖方的偏好构成了供给，而两者结合起来决定了商品在任意市场形态中的价格和数量。
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.
在一个资本主义社会中，价格并不是由一个中央权威制定的，而是这些市场中买方和卖方互动的结果。
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.
不过，这里和有形的市场不同，买方和卖方并不需要同时处在一个地方，他们只需要期望进行同一场经济交易即可。
It’s important to keep in mind that prices and quantities are the outputs of the supply and demand model, not the inputs.
有一个很重要的点需要记住，那就是：价格与数量都是由供给需求模型决定的结果，而不是它的决定因素。
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.
还有一点很重要的是：供给需求模型仅适用于竞争性市场——也就是有很多买方和卖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.
那些不满足这些要求的市场则适用不同的模型。
The Law of Supply and The Law of Demand
供给需求模型的法则
The supply and demand model can be broken into two parts: the law of demand and the law of supply.
供给需求模型可以被分解成两个法则：需求法则和供给法则。
In the law of demand, the higher a supply’s price, the lower the quantity of demand for that product becomes.
根据需求法则，一种产品的价格越高，对这种产品的需求量就越小。
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.”
法则本身的说法是“在其他一切变量不变的前提下，当一件产品的价格升高，对其的需求量就会下降；相反，当一件产品的价格降低，对其的需求量就会增加。”
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.
这主要关系到买方买这种更贵产品时需要付出的机会成本，这其中的思路是：买方需要放弃购买某些他们觉得更有价值的东西来购买这件更贵的产品，所以他们可能会减少对它的购买量。
Similarly, the law of supply correlates to the quantities that will be sold at certain price points.
相似地，需求法则主要关系到在不同价位点会被售出的产品数量。
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.
供给模型从根本上来说是和需求模型相反的，它展现出的规律是：价格越高，供给量也越高，因为当价格和销量越高时，企业的盈利也就越高。
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.
供给与需求的关系非常有效地导致两者取得了一个平衡点，在这一点上，市场中的供给恰好等于需求。
Application in Modern Economics
（供给需求模型）在现代经济学中的应用
To think of it in modern application, take the example of a new DVD being released for $15.
要想看它的现代版实例，我们来看一种定价为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.
由于市场分析显示目前的消费者不会付出比这更高的价格来看一部电影，所以公司决定把这个DVD发行100份；因为，对于当前的需求量来说，供应方制造更多DVD的机会成本太高了。
However, if the demand rises, the price will also increase resulting in a higher quantity supply.
不过，当需求升高时，DVD的价格也会上升，然后就会导致供给量也上升。
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发行了100份，而需求只有50份，价格就会下降以求售出那剩下的50份市场并不需要的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.
供给需求模型的核心概念给现代经济学的各种讨论奠定了基础，对于资本主义社会尤其如此。
Without a fundamental understanding of this model, it is almost impossible to understand the complex world of economic theory.
如果不能理解这个基础概念，那几乎就不可能理解经济学世界中的复杂理论。
