From an e conomist's perspective, making choices involves making decisions 'at the margin' -- that is, making decisions based on small changes in resources:

从经济学家的角度来看，做出选择包括“在边际”做出决定——也就是说，根据资源的微小变化做出决定：

How should I spend the next hour?

我该如何度过接下来的一个小时?

How should I spend the next dollar?

下一美元该怎么花?

In fact, e conomist Greg Mankiw lists under the "10 principles of economics" in his popular economics textbook the notion that "rational people think at the margin." On the surface, this seems like a strange way of considering the choices made by people and firms.

事实上，经济学家格雷格·曼昆在他广受欢迎的经济学教科书中的“经济学的十大原则”下列出了“理性的人在边缘思考”。从表面上看，这似乎是一种奇怪的方式来考虑人们和公司做出的选择。

It is rare that someone would consciously ask themselves -- "How will I spend dollar number 24,387?" or "How will I spend dollar number 24,388?" The idea of marginal analysis doesn't require that people explicitly think in this way, just that their actions are consistent with what they would do if they did think in this way.  

很少有人会有意识地问自己——“我将如何花24,387美元?”或者“我将如何花24,388美元?”边际分析的思想并不要求人们明确地以这种方式思考，只要求他们的行为与他们以这种方式思考会做的事情是一致的。

Marginal analysis can be applied to both individual and firm decision making.

边际分析既适用于个人决策，也适用于企业决策。

For firms, profit maximization is achieved by weighing marginal revenue versus marginal cost.

对于企业来说，利润最大化是通过权衡边际收益与边际成本来实现的。

For individuals, utility maximization is achieved by weighing the marginal benefit versus marginal cost. Note, however, that in both contexts the decision maker is performing an incremental form of cost-benefit analysis.

对个人来说，效用最大化是通过权衡边际效益和边际成本来实现的。但请注意，在这两种情况下，决策者都在执行一种增量形式的成本效益分析。

Let’s see an example:

让我们来看一个例子：

To gain some more insight, consider the decision regarding how many hours to work, where the benefits and costs of working are designated by the following chart:

为了更深入的了解，我们来权衡一下关于工作时间的决定，工作的收益和成本是由下面的图表指定的:

Hour - Hourly Wage - value of Time

工作时间 - 每小时的工资 - 时间的价值

The hourly wage represents what one earns for working an extra hour - it is the marginal gain or the marginal benefit.

每小时的工资代表了一个人额外工作一小时的收入——这是边际收益或边际效益。

The value of time is essentially an opportunity cost -- it is how much one values having that hour off. In this example, it represents a marginal cost -- what it costs an individual to work an additional hour. The increase in marginal costs is a common phenomenon; one usually doesn't mind working a few hours since there are 24 hours in a day. She still has plenty of time to do other things. However, as an individual starts to work more hours, it reduces the number of hours she has for other activities. She has to start giving up more and more valuable opportunities to work those extra hours.

时间的价值本质上是一个机会成本——它是一个人休息一个小时的价值。在这个例子中，它代表了边际成本——一个人额外工作一小时的成本。边际成本的增加是一个普遍现象；人们通常不介意工作几个小时，因为一天有24小时，她还有足够的时间做其他事情。然而，当一个人开始工作更长时间时，这就减少了她从事其他活动的时间。她不得不开始放弃越来越多的宝贵机会来加班。

It is clear that she should work the first hour, as she gains $10 in marginal benefits and loses only $2 in marginal costs, for a net gain of $8.

显然，她应该在第一个小时工作，因为她的边际收益是10美元，而边际成本只有2美元，净收益是8美元。

By the same logic, she should work the second and third hours as well. She will want to work until the time at which the marginal cost exceeds the marginal benefit. She will also want to work the 10th hour as she receives a net benefit of $3 (marginal benefit of $15, marginal cost of $12). However, she will not want to work the 11th hour, as the marginal cost ($18) exceeds the marginal benefit ($15) by three dollars.

按照同样的逻辑，她也应该在第2和第3个小时工作。她会一直工作到边际成本超过边际效益的时候。到第10个小时的时候她还是愿意工作，因为她的净收益为3美元(边际收益为15美元，边际成本为12美元)。然而，第11个小时的工作她就不会愿意做了，因为边际成本(18美元)比边际效益(15美元)还要高出3美元。

Thus marginal analysis suggests that rational maximizing behavior is to work for 10 hours. More generally, optimal outcomes are achieved by examining marginal benefit and marginal cost for each incremental action and performing all of the actions where marginal benefit exceeds the marginal cost and none of the actions where marginal cost exceeds the marginal benefit. Because marginal benefits tend to decrease as one does more of an activity but marginal costs tend to increase, the marginal analysis will usually define a unique optimal level of activity.

因此，边际分析表明，合理的最大化行为是工作10小时。更笼统的说，通过检查每个增量行动的边际效益和边际成本，并执行边际效益超过边际成本的所有行动，以及边际成本没有超过边际效益的任何行动，均可获得最佳结果。因为边际收益会随着一项活动的增加而减少，而边际成本却增加，因此边际分析通常会定义一个唯一的最佳活动水平。