在帕金和巴德的经济学教材中，对商业周期给出了以下定义：
"The business cycle is the periodic but irregular up-and-down movements in economic activity，measured by fluctuations in real GDP and other macroeconomic variables."
“商业周期是经济活动的周期性但不规则的上下波动，以实际GDP和其他宏观经济变量的波动来衡量。”
To put it simply，the business cycle is defined as the real fluctuations in economic activity and gross domestic product (GDP) over a period of time. The fact that the economy experiences these ups-and-downs in activity should be no surprise. In fact，all modern industrial economies like that of the United States endure considerable swings in economic activity over time.
The ups may be marked by indicators like high growth and low unemployment while the downs are generally defined by low or stagnant growth and high unemployment. Given its relationship to the phases of the business cycle，unemployment is but one of the various economic indicators used to measure economic activity. For most detailed information about how various economic indicators and their relationship to the business cycle，check out A Beginner's Guide to Economic Indicators.
高增长和低失业率等指标可能标志着经济复苏，而经济低迷通常由低增长或停滞增长以及高失业率来定义。鉴于失业与商业周期各阶段的关系，失业只是用来衡量经济活动的各种经济指标之一。有关各种经济指标及其与商业周期的关系的最详细信息，请参阅《经济指标入门指南》。
Parkin and Bade go on to explain that despite the name，the business cycle is not a regular，predictable，or repeating the cycle. Though its phases can be defined，its timing is random and，to a large degree，unpredictable.
帕金和巴德继续解释道，尽管名字中有周期二字，但商业周期并不是一个规律的、可预测的或重复的循环。虽然它的阶段可以被定义，但其时间是随机的，并且在很大程度上是不可预测的。
The Phases of the Business Cycle
商业周期的各个阶段
While no two business cycles are exactly the same，they can be identified as a sequence of four phases that were classified and studied in their most modern sense by American e·conomists Arthur Burns and Wesley Mitchell in their text "Measuring Business Cycles." The four primary phases of the business cycle include:
虽然没有两个商业周期是完全相同的，而根据美国经济学家阿瑟•伯恩斯和卫斯理•米切尔在他们的著作《衡量商业周期》中最前沿的分类和研究，一个周期通常可以分为四个阶段，大致包括：
Expansion:A speedup in the pace of economic activity defined by high growth，low unemployment，and increasing prices. The period marked from trough to peak.
扩张：经济增长速度加快，由高增长、低失业率和物价上涨所决定。包括从低谷到高峰的时期。
Peak:The upper turning point of a business cycle and the point at which expansion turns into contraction.
峰值：商业周期的上升拐点和收缩拐点。
Contraction: A slowdown in the pace of economic activity defined by low or stagnant growth，high unemployment，and declining prices. It is the period from peak to trough.
收缩：经济活动放缓，由低增长或停滞增长，高失业率和价格下降所决定。包括从峰值到低谷的时期。
Trough: The lowest turning point of a business cycle in which a contraction turns into an expansion. This turning point is also called Recovery.
低谷：商业周期中收缩转变为扩张的最低拐点。这个拐点也称为复苏。
These four phases also make up what is known as the "boom-and-bust" cycles，which are characterized as business cycles in which the periods of expansion are swift and the subsequent contraction is steep and severe.
这四个阶段也构成了所谓的“繁荣与萧条”周期，其特征扩张迅速，收缩陡峭的商业周期。
But What About Recessions?
但是经济衰退呢？
1 一个原本普通的母亲，因为有了一个双腿残疾的儿子而备受煎熬。遭受打击的儿子，原本只以为这煎熬是属于他的，后来他才明白这煎熬在他的母亲那里是成倍地增加。双腿残疾后，史铁生一下子被击垮了，他愤怒、狂躁，怨天尤人。
A recession occurs if a contraction is severe enough. The National Bureau of Economic Research (NBER) identifies a recession as a contraction or significant decline in economic activity "lasting more than a few months，normally visible in real GDP，real income，employment，industrial production."
如果收缩足够严重，就会出现衰退。美国国家经济研究局认为经济衰退是经济活动的收缩或显著下降“持续几个月以上，通常可见于实际GDP、实际收入、就业和工业生产中。”
《我与地坛》是带有自传、自省、自述意味的散文,史铁生以真实的身份投入作品,用文字坦诚地表现自己在地坛沉思流连所观察到的人生百态和对命运的感悟,作者由个人严酷的命运上升到生命永恒的流变,超越了个体生命有限的必然,把自己的沉思带入。
Along the same vein，a deep trough is called a slump or a depression. The difference between a recession and a depression，which is not well-understood by non-e·conomists，is explained in this helpful guide: Recession? Depression? What's the difference?
The Great Recession
经济大衰退
The Great Recession was a period of general economic decline observed in world markets during the late 2000s and early 2010s.
“大衰退”指的是20世纪末至2010年初全球市场普遍出现的经济衰退时期。
The scale and timing of the recession varied from country to country. The International Monetary Fund concluded that the overall impact was the most severe since the Great Depression in the 1930s.
《钢铁是怎样炼成的》第九章感悟是我缓缓合上《钢铁是怎样炼成的》，书中的情节令我铭刻肺腑。保尔早年丧父。被赶出学校后，当了两年杂役才转到发电厂。革命爆发后，他结识了老布尔什维克朱赫来，埋下革命的种子。他敢于向。
经济衰退的规模和时机因国而异。国际货币基金组织得出的结论是，自上世纪30年代大萧条以来，“大衰退”的总体影响最为严重。
The Great Recession stemmed from collapse of the United States real-estate market，in relation to the financial crisis of 2007 to 2008 and U.S. subprime mortgage crisis of 2007 to 2009，though policies of other nations contributed also. According to the U.S. National Bureau of Economic Research (the official arbiter of U.S. recessions) the US recession began in December 2007 and ended in June 2009，thus extending over 19 months.
大萧条源于美国房地产市场的崩溃，与2007-2008年的金融危机和2007-2009年的美国次贷危机有关，尽管其他国家的政策也起到了一定作用。根据美国国家经济研究局（美国经济衰退的官方仲裁机构）的数据，美国经济衰退始于2007年12月，结束于2009年6月，持续了19个月的时间。
The Great Recession resulted in the scarcity of valuable assets in the market economy and the collapse of the financial sector (banks) in the world economy. The banks were then bailed out by the U.S. government.
大萧条导致了市场经济中宝贵资产的稀缺和世界经济中金融部门（银行）的崩溃。随后这些银行得到了美国政府的救助。
作为一只猪，悲痛欲绝的威尔伯似乎只能接受任人宰割的命运了。然而看似渺小的小蜘蛛夏洛却说：“我救你。”于是，夏洛在猪栏上织出了被人类视为奇迹的网上文字，这些赞美威尔伯的文字彻底改变了威尔伯的命运，终于让威尔伯在集市。
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