A level 经济学（国际课程A-level经济）

In the last Learn-It, we looked at demand and in particular, consumers' effective demand for various goods and services. When it comes to supply, we are talking about how much of a given product the sellers, or firms, or producers are prepared to supply to the market at any given price.

在上一期的学习中，我们研究了需求，特别是消费者对各种商品和服务的有效需求。谈到供应，我们谈论的是卖家，或公司，或生产商准备以任何特定的价格向市场供应多少特定的产品。

Just like with demand, where it only became effective if it was backed up with the ability to pay, supply is defined as the willingness and ability of producers to supply goods and services on to a market at a given price in a given period of time. With demand, the downward-sloping curve reflected an inverse relationship between price and quantity demanded. The opposite is true of supply.

In theory, at higher prices a larger quantity will generally be supplied than at lower prices, ceteris paribus, and at lower prices a smaller quantity will generally be supplied than at higher prices, ceteris paribus. So this time we have higher supply at higher prices and vice versa. Again, in is important to assume that 'all other things remain constant'. Any change in one of the other determinants of supply will cause the curve to shift (see below).

正如需求只有在有支付能力的支持下才会有效一样，供应被定义为生产者在一定时期内以特定价格向市场提供商品和服务的意愿和能力。对于需求来说，向下倾斜的曲线反映了价格和需求量之间的反比关系。而供应则相反。

从理论上讲，在较高的价格下，通常会比在较低的价格下供应更多的数量，在较低的价格下，通常会比在较高的价格下供应更少的数量，其他情况也是如此。因此，这次我们在价格较高时有较高的供应量，反之亦然。同样，重要的是要假设 "所有其他事情保持不变"。供应的其他决定因素之一的任何变化都将导致曲线的移动（见下文）。

The upward sloping supply curve can be seen below 下面可以看到向上倾斜的供应曲线:

While it is fairly obvious why the demand curve is downward sloping, it is not so clear why the supply curve should be upward sloping. Basically, the producer will make higher profits as the price per unit sold increases. Imagine that a brewer produced a lager and a bitter. Assume, not unreasonably, that the costs of production are the same per pint produced, whether it is a pint of lager or a pint of bitter. If the price of lager then rose relative to the price of bitter, it would seem sensible for the brewer to transfer resources from making bitter towards the production of lager, thereby increasing the supply of lager as its price rises.

虽然需求曲线向下倾斜的原因相当明显，但供给曲线为什么要向上倾斜就不太清楚了。基本上，随着每单位销售价格的提高，生产商将获得更高的利润。想象一下，一个酿酒商生产一种拉格酒和一种苦啤酒。不无道理地假设，无论是一品脱的拉格酒还是一品脱的苦啤酒，每品脱的生产成本都是一样的。如果拉格酒的价格相对于苦啤酒的价格上涨，那么啤酒商将生产苦啤酒的资源转移到拉格酒的生产上，从而在拉格酒的价格上涨时增加拉格酒的供应，这似乎是明智的。

As with the demand curve, there are many things that affect supply as well as the price of the good in question. Notice how similar many of these factors are in comparison to the factors that affect demand. Notice also that nearly all of these factors affect the firms' costs. Given that the firms' supply curve is its marginal cost curve (see the 'costs and revenues' topic) then it is of no surprise that a cost changing measure will shift the supply curve.

与需求曲线一样，有许多因素会影响供应以及有关商品的价格。请注意，与影响需求的因素相比，其中许多因素是多么相似。还请注意，几乎所有这些因素都会影响企业的成本。鉴于企业的供给曲线是它的边际成本曲线（见 "成本和收入 "专题），那么，成本变化的措施会使供给曲线发生变化，这并不奇怪。

1. Prices of other factors of production. An increase in the price of, say, hops, will increase the costs of a brewing firm and so for any given price the firm will not be able to brew as much beer. Hence, the firm's supply curve will shift to the left. The same would be true for changes in wage costs or fuel costs.
2. Technology. The supply curve drawn above assumes a 'constant' state of technology. But as we know, there can be improvements in technology that tend to reduce firms' unit costs. These reduced costs mean that more can be produced at a given price, so the supply curve would shift to the right.
3. Indirect taxes and subsidies. When the chancellor announces an increase in petrol tax (again!), it is the firm who actually pays the tax. Granted, we end up paying the tax indirectly when the price of petrol goes up, but the actual tax bill goes to the firm. This again, therefore, represents an increase in the cost to the firm and the supply curve will shift to the left. The opposite is true for subsidies as they are handouts by the government to firms. Now the firm can make more units of output at any given price, so the supply curve shifts to the right.
4. Labour productivity. This is defined as the output per worker (or per man-hour). If labour productivity rises, then output per worker rises. If you assume that the workers have not been given a pay rise then the firm's unit costs must have fallen. Again, this will lead to a shift to the right of the supply curve.
5. Price expectations. Just as consumers delay purchases if they think the price will fall in the future, firms will delay supply in they think prices will rise in the future. It's the same point but the other way round.
6. Entry and exit of firms to and from an industry. If new entrants are attracted into an industry, perhaps because of high profit levels (much more on this in the topic 'Market structure'), then the supply in that industry will rise at all price levels and the supply curve will shift to the right. If firms leave the industry then the supply curve will shift to the left.

其他生产要素的价格：例如，啤酒花价格的提高将增加酿酒公司的成本，因此在任何给定的价格下，该公司将无法酿造出那么多的啤酒。因此，该公司的供应曲线将向左移动。工资成本或燃料成本的变化也是如此。

技术：上面所画的供给曲线假定了技术的 "恒定 "状态。但正如我们所知，技术的改进往往会降低企业的单位成本。这些成本的降低意味着在给定的价格下可以生产更多的产品，所以供应曲线会向右移动。

间接税和补贴：当财政大臣宣布增加汽油税时（又一次！），实际支付税款的是企业。诚然，当汽油价格上涨时，我们最终间接地支付了税款，但实际的税单是由公司支付的。因此，这又代表了企业成本的增加，供应曲线将向左移动。补贴的情况则相反，因为它们是政府对企业的施舍。现在，企业可以在任何给定的价格下生产更多的产出单位，所以供给曲线会向右移动。

劳动生产率：这被定义为每个工人（或每个工时）的产出。如果劳动生产率提高了，那么每个工人的产出就会提高。如果你假设工人没有得到加薪，那么公司的单位成本一定会下降。同样，这将导致供给曲线向右移动。

价格预期：就像消费者认为价格在未来会下降而推迟购买一样，企业认为价格在未来会上升而推迟供应。这是同一点，但反过来说。

企业进入和退出一个行业：如果新进入者被吸引到一个行业，也许是因为高利润水平（在 "市场结构 "这一主题中会有更多的介绍），那么该行业的供应在所有价格水平上都会上升，供应曲线会向右移动。如果企业离开这个行业，那么供给曲线将向左移动。

As with demand, we must now look at the difference between a movement along a supply curve and a shift of a supply curve. Those of you who have looked at the 'Demand curve' Learn It should know exactly what is coming next!

与需求一样，我们现在必须看一下沿着供给曲线的移动和供给曲线的移动之间的区别。那些看过 "需求曲线 "的人应该很清楚接下来会发生什么。

If you understand this topic when it is related to the demand curve then you will be fine here as well. The principles are exactly the same. A movement along a supply curve only occurs when the price changes, ceteris paribus. In other words, the price changes but the other non-price determinants remain constant. The diagram below shows that a price rise will cause an extension up the supply curve, from point A to point B, whilst a price fall will cause a contraction back down the supply curve, from point A to point C.

如果你理解了这个与需求曲线有关的主题，那么你在这里也会很好。原则是完全一样的。只有当价格发生变化时，才会出现沿着供给曲线的移动，这是个例外情况。换句话说，价格变化，但其他非价格决定因素保持不变。下图显示，价格上涨将导致供应曲线向上延伸，从A点到B点，而价格下跌将导致供应曲线向下收缩，从A点到C点。

As with shifts of demand curves, supply curves shift, at all prices, if there is a change in one or more of the determinants of supply. As stated above, nearly all the determinants of supply affect the costs of the firm and, therefore, its supply curve, which is its marginal cost curve. Put simply, if something happens that increases a firm's costs regardless of the price level (e.g. an increase in the wage rate, of an increase in government taxes), then the firm's supply curve will shift to the left. If something happens that decreases a firm's costs regardless of the price level (e.g. improved technology or a subsidy from the government), then the firm's supply curve shifts to the right. The diagram below demonstrates these shifts:

与需求曲线的移动一样，如果供应的一个或多个决定因素发生变化，供应曲线也会在所有价格上发生移动。如上所述，几乎所有的供应决定因素都会影响企业的成本，因此，其供应曲线也就是其边际成本曲线。简单地说，如果发生了一些事情，使企业的成本增加，而不管价格水平如何（例如，工资率的增加，政府税收的增加），那么企业的供应曲线将向左移动。如果发生了一些事情，使企业的成本降低，而不管价格水平如何（例如，技术的改进或政府的补贴），那么企业的供应曲线就会向右移动。下图展示了这些变化：

Note that the price remains unchanged at P1; the shifts in the supply curve are caused by various changes in the determinants of supply. Try the following exercise to make sure that you understand why a firm's supply curve shifts. Remember that the initial position of the supply curve is S1. Click on the curve to which you think the supply curve shifts.

请注意，价格在P1处保持不变；供应曲线的移动是由供应的决定因素的各种变化引起的。试试下面的练习，以确保你理解企业的供给曲线为什么会发生变化。记住，供给曲线的初始位置是S1。点击你认为供给曲线会向哪个方向移动的曲线。