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.

在上一期的學習中，我們研究了需求，特別是消費者對各種商品和服務的有效需求。談到供應，我們談論的是賣家，或公司，或生產商準備以任何特定的價格向市場供應多少特定的產品。

The theory of supply 供應的理論

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會有效一樣，供應被定義為生產者在一定時期內以特定價格向市場提供商品和服務的意愿和能力。對于需求來說，向下傾斜的曲線反映了價格和需求量之間的反比關系。而供應則相反。

從理論上講，在較高的價格下，通常會比在較低的價格下供應更多的數量，在較低的價格下，通常會比在較高的價格下供應更少的數量，其他情況也是如此。因此，這次我們在價格較高時有較高的供應量，反之亦然。同樣，重要的是要假設 "所有其他事情保持不變"。供應的其他決定因素之一的任何變化都將導致曲線的移動（見下文）。

The upward sloping supply curve can be seen below 下面可以看到向上傾斜的供應曲線:

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.

雖然需求曲線向下傾斜的原因相當明顯，但供給曲線為什么要向上傾斜就不太清楚了?；旧?，隨著每單位銷售價格的提高，生產商將獲得更高的利潤。想象一下，一個釀酒商生產一種拉格酒和一種苦啤酒。不無道理地假設，無論是一品脫的拉格酒還是一品脫的苦啤酒，每品脫的生產成本都是一樣的。如果拉格酒的價格相對于苦啤酒的價格上漲，那么啤酒商將生產苦啤酒的資源轉移到拉格酒的生產上，從而在拉格酒的價格上漲時增加拉格酒的供應，這似乎是明智的。

The determinants of supply 供應的決定因素

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.

與需求曲線一樣，有許多因素會影響供應以及有關商品的價格。請注意，與影響需求的因素相比，其中許多因素是多么相似。還請注意，幾乎所有這些因素都會影響企業(yè)的成本。鑒于企業(yè)的供給曲線是它的邊際成本曲線（見 "成本和收入 "專題），那么，成本變化的措施會使供給曲線發(fā)生變化，這并不奇怪。

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.

其他生產要素的價格：例如，啤酒花價格的提高將增加釀酒公司的成本，因此在任何給定的價格下，該公司將無法釀造出那么多的啤酒。因此，該公司的供應曲線將向左移動。工資成本或燃料成本的變化也是如此。

技術：上面所畫的供給曲線假定了技術的 "恒定 "狀態(tài)。但正如我們所知，技術的改進往往會降低企業(yè)的單位成本。這些成本的降低意味著在給定的價格下可以生產更多的產品，所以供應曲線會向右移動。

間接稅和補貼：當財政大臣宣布增加汽油稅時（又一次！），實際支付稅款的是企業(yè)。誠然，當汽油價格上漲時，我們最終間接地支付了稅款，但實際的稅單是由公司支付的。因此，這又代表了企業(yè)成本的增加，供應曲線將向左移動。補貼的情況則相反，因為它們是政府對企業(yè)的施舍?，F(xiàn)在，企業(yè)可以在任何給定的價格下生產更多的產出單位，所以供給曲線會向右移動。

勞動生產率：這被定義為每個工人（或每個工時）的產出。如果勞動生產率提高了，那么每個工人的產出就會提高。如果你假設工人沒有得到加薪，那么公司的單位成本一定會下降。同樣，這將導致供給曲線向右移動。

價格預期：就像消費者認為價格在未來會下降而推遲購買一樣，企業(yè)認為價格在未來會上升而推遲供應。這是同一點，但反過來說。

企業(yè)進入和退出一個行業(yè)：如果新進入者被吸引到一個行業(yè)，也許是因為高利潤水平（在 "市場結構 "這一主題中會有更多的介紹），那么該行業(yè)的供應在所有價格水平上都會上升，供應曲線會向右移動。如果企業(yè)離開這個行業(yè)，那么供給曲線將向左移動。

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!

與需求一樣，我們現(xiàn)在必須看一下沿著供給曲線的移動和供給曲線的移動之間的區(qū)別。那些看過 "需求曲線 "的人應該很清楚接下來會發(fā)生什么。

Movements along a supply curve 沿著供給曲線的移動

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.

如果你理解了這個與需求曲線有關的主題，那么你在這里也會很好。原則是完全一樣的。只有當價格發(fā)生變化時，才會出現(xiàn)沿著供給曲線的移動，這是個例外情況。換句話說，價格變化，但其他非價格決定因素保持不變。下圖顯示，價格上漲將導致供應曲線向上延伸，從A點到B點，而價格下跌將導致供應曲線向下收縮，從A點到C點。

Shifts of a supply curve 供應曲線的移動

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:

與需求曲線的移動一樣，如果供應的一個或多個決定因素發(fā)生變化，供應曲線也會在所有價格上發(fā)生移動。如上所述，幾乎所有的供應決定因素都會影響企業(yè)的成本，因此，其供應曲線也就是其邊際成本曲線。簡單地說，如果發(fā)生了一些事情，使企業(yè)的成本增加，而不管價格水平如何（例如，工資率的增加，政府稅收的增加），那么企業(yè)的供應曲線將向左移動。如果發(fā)生了一些事情，使企業(yè)的成本降低，而不管價格水平如何（例如，技術的改進或政府的補貼），那么企業(yè)的供應曲線就會向右移動。下圖展示了這些變化：

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.

請注意，價格在P1處保持不變；供應曲線的移動是由供應的決定因素的各種變化引起的。試試下面的練習，以確保你理解企業(yè)的供給曲線為什么會發(fā)生變化。記住，供給曲線的初始位置是S1。點擊你認為供給曲線會向哪個方向移動的曲線。

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