【文章內(nèi)容簡(jiǎn)介】 flexible. Just as a physicist uses different assumptions when studying falling marbles and falling beach balls, economists use different assumptions when studying the shortrun and longrun effects of a change in the quantity of money.相似地，經(jīng)濟(jì)學(xué)家用不同的假設(shè)來(lái)回答不同的問(wèn)題。假設(shè)我們要研究當(dāng)政府改變流通中的貨幣時(shí)，會(huì)對(duì)經(jīng)濟(jì)產(chǎn)生什么樣的影響。結(jié)果表明，這個(gè)分析很重要的一條是價(jià)格是如何回應(yīng)的。經(jīng)濟(jì)中很多價(jià)格會(huì)經(jīng)常變動(dòng)，報(bào)攤上的雜志價(jià)格變動(dòng)會(huì)隔幾年。懂得這一事實(shí)，可以讓我們?cè)谘芯坎煌瑫r(shí)期政策改變的影響時(shí)，做出不同的假設(shè)。對(duì)于研究政策的短期影響時(shí)，我們可以假設(shè)價(jià)格不會(huì)變動(dòng)很大。我們甚至可以做極端人為的假設(shè)——所有價(jià)格都完全不變。然而，對(duì)于研究政策的長(zhǎng)期影響，我們可以假設(shè)所有價(jià)格都是完全彈性的。就像物理學(xué)家研究大理石降落和沙灘排球降落用不同的假設(shè)一樣，經(jīng)濟(jì)學(xué)家在研究貨幣量變化的短期和長(zhǎng)期影響時(shí)，用不同的假設(shè)。ECONOMIC MODELS經(jīng)濟(jì)模型High school biology teachers teach basic anatomy with plastic replicas of the human body. These models have all the major organs—the heart, the liver, the kidneys, and so on. The models allow teachers to show their students in a simple way how the important parts of the body fit together. Of course, these plastic models are not actual human bodies, and no one would mistake the model for a real person. These models are stylized, and they omit many details. Yet despite this lack of realism—indeed, because of this lack of realism—studying these models is useful for learning how the human body works.高中生物老師用人體的塑料復(fù)制品講授基礎(chǔ)解剖學(xué)。這些模型都有主要的器官：心臟、肝臟、腎臟等等。這些模型讓老師用簡(jiǎn)單的方式展示給他們的學(xué)生身體上這些重要的部分是如何互相協(xié)調(diào)的。當(dāng)然，這些塑料模型不是真實(shí)的人體，沒(méi)有人會(huì)把這些模型誤認(rèn)為是真的人。這些模型是設(shè)計(jì)的，他們忽略了很多細(xì)節(jié)。然而，盡管缺乏真實(shí)性，但是正是對(duì)這些模型的研究，對(duì)學(xué)習(xí)人體如何工作很有幫助。Economists also use models to learn about the world, but instead of being made of plastic, they are most often posed of diagrams and equations. Like a biology teacher’s plastic model, economic models omit many details to allow us to see what is truly important. Just as the biology teacher’s model does not include all of the body’s muscles and capillaries, an economist’s model does not include every feature of the economy.經(jīng)濟(jì)學(xué)家也用模型來(lái)學(xué)習(xí)世界，但是他們通常用圖表和等式，而不是制作塑料復(fù)制品。就像一個(gè)生物老師的塑料模型，經(jīng)濟(jì)模型忽略了很多細(xì)節(jié)，這些細(xì)節(jié)可以讓我們看到什么是真正重要的。就像生物老師的模型不包括人體所有的肌肉和毛細(xì)血管一樣，經(jīng)濟(jì)學(xué)家的模型不包括經(jīng)濟(jì)的每個(gè)特征。As we use models to examine various economic issues throughout this book, you will see that all the models are built with assumptions. Just as a physicist begins the analysis of a falling marble by assuming away the existence of friction, economists assume away many of the details of the economy that are irrelevant for studying the question at hand. All models—in physics, biology, or economics— simplify reality in order to improve our understanding of it.整本書中我們用模型來(lái)解決不同的經(jīng)濟(jì)問(wèn)題，你會(huì)看到所有的模型都是基于一定的假設(shè)。就像物理學(xué)家對(duì)下落的大理石假設(shè)不存在摩擦力進(jìn)行分析一樣，經(jīng)濟(jì)學(xué)家假設(shè)忽略了很多與問(wèn)題研究不相關(guān)的細(xì)節(jié)。所有的模型不論是物理、生物、還是經(jīng)濟(jì)學(xué)，都簡(jiǎn)化了現(xiàn)實(shí)，以提高我們對(duì)問(wèn)題的理解。OUR FIRST MODEL: THE CIRCULARFLOW DIAGRAM第一個(gè)模型：循環(huán)流向圖The economy consists of millions of people engaged in many activities—buying, selling, working, hiring, manufacturing, and so on. To understand how the economy works, we must find some way to simplify our thinking about all these activities. In other words, we need a model that explains, in general terms, how the economy is organized and how participants in the economy interact with one another.經(jīng)濟(jì)由成千上萬(wàn)的人組成，這些人參加很多活動(dòng)：購(gòu)買、銷售、工作、雇傭、制造等等。為了理解經(jīng)濟(jì)如何工作，我們必須找到一種方法來(lái)簡(jiǎn)化我們對(duì)這些活動(dòng)的思考。換句話說(shuō)，我們需要一個(gè)模型，這個(gè)模型能夠用普通詞匯解釋經(jīng)濟(jì)是如何組織的，經(jīng)濟(jì)的參加者是如何相互影響的。Figure 21 presents a visual model of the economy, called a circularflow diagram. In this model, the economy has two types of decisionmakers—households and firms. Firms produce goods and services using inputs, such as labor, land, and capital (buildings and machines). These inputs are called the factors of production. Households own the factors of production and consume all the goods and services that the firms produce.圖21展示了經(jīng)濟(jì)的一個(gè)可視化模型，被稱為循環(huán)流向圖。在這個(gè)模型中，經(jīng)濟(jì)有兩種類型的決策者：家庭和公司。公司通過(guò)勞動(dòng)、土地及資本（大樓和機(jī)器）的輸入來(lái)生產(chǎn)貨物和服務(wù)。這些輸入被稱為生產(chǎn)因素。家庭擁有生產(chǎn)要素并且消費(fèi)公司生產(chǎn)的所有貨物和服務(wù)。Households and firms interact in two types of markets. In the markets for goods and services, households are buyers and firms are sellers. In particular, households buy the output of goods and services that firms produce. In the markets for the factors of production, households are sellers and firms are buyers. In these markets, households provide firms the inputs that the firms use to produce goods and services. The circularflow diagram offers a simple way of organizing all the economic transactions that occur between households and firms in the economy.家庭和公司在兩種類型的市場(chǎng)上互相影響。在貨物和服務(wù)市場(chǎng)上，家庭是購(gòu)買者，公司是賣者。特別的是，家庭購(gòu)買公司生產(chǎn)并輸出的貨物和服務(wù)。在生產(chǎn)要素市場(chǎng)上，家庭是賣者，公司是買者。在這些市場(chǎng)上，家庭提供公司生產(chǎn)貨物和服務(wù)的輸入原料。這個(gè)循環(huán)流向圖提供家庭和公司之間組織經(jīng)濟(jì)交易的一種簡(jiǎn)單方式。The inner loop of the circularflow diagram represents the flows of goods and services between households and firms. The households sell the use of their labor, land, and capital to the firms in the markets for the factors of production. The firms then use these factors to produce goods and services, which in turn are sold to households in the markets for goods and services. Hence, the factors of production flow from households to firms, and goods and services flow from firms to households.循環(huán)流向圖的里面一圈代表家庭和公司間貨物和服務(wù)的流動(dòng)。家庭把他們的勞動(dòng)、土地及資本賣給公司，以作為公司的生產(chǎn)要素。然后公司用這些要素來(lái)生產(chǎn)貨物和服務(wù)，反過(guò)來(lái)又把這些貨物和服務(wù)在市場(chǎng)上賣給家庭。因此，生產(chǎn)要素從家庭流動(dòng)到公司，貨物和服務(wù)從公司流動(dòng)到家庭。The outer loop of the circularflow diagram represents the corresponding flow of dollars. The households spend money to buy goods and services from the firms. The firms use some of the revenue from these sales to pay for the factors of production, such as the wages of their workers. What’s left is the profit of the firm owners, who themselves a