生产可能性是经济学里一个比较难的概念。我没有逐字按原文翻译，而是为了便于理解改变了顺序，并加入了很多经济学的例子。希望大家记住我们学英语的最根本目的：为了使用。

在我们研究的整个社会模型中，生产可能性曲线，或称生产可能性边界是一条固定的曲线。前提是假设资源固定，而人的选择就是这条固定曲线上的某一点。也就说，选择的可能只能是在这条曲线上来回的移动，而不能离开这条曲线。

我们先来快速回忆一下资源的几种分类：自然资源，人力资源，资本资源和企业家资源。（参考前文）

记得吗？土地是一种自然资源，劳动力是一种人力资源，工厂和设备是一种资本资源（固定资产，或有形资产。这里资本不仅仅指金钱），最后是企业家资源。再强调一下企业家能力：企业家是指具有以下能力的人： 1. 盈利能力。2. 愿意承担风险的能力。 3. 能够调配资源的能力。

我们说生产可能性曲线是固定的。是假定资源固定的情况下。什么意思呢？比如同样的时间，同样的工人劳力，企业家可以选择生产电脑生产小麦。但选择生产电脑的资源就不能再用来生产小麦，这就是资源固定的意思。如果我们进一步思考，有些资源可能更适合生产小麦，而不是电脑。如果你说当然是生产电脑更赚钱啦，于是将水，甚至农药等本来更适合生产小麦的资源来制造电脑，那我们可以想象是非常低效率的，甚至是无用的。你是在浪费资源。

那么，从生产可能性理论出发，有没有什么资源不是固定的情况呢？ 还有，当资源改变的时候，生产可能性将如何改变呢？

记得经济学家常说的那句话吗？ 看情况。

有一种情况下曲线是会变化的。小麦和电脑的区别一个是劳动密集型的农业生产，一个是资本密集型的工业生产。如果现在忽然有个教授研制出一种非常高效的化肥，能让小麦生产翻番。那么此时生产可能性曲线将向外移动。表现在坐标系上，就是这条红色的曲线，其他资源不变，生产出了更多的产品。

那这个例子对我们有什么启发呢？

同样的化肥如果用于生产电脑呢？还会产生双倍的产量吗？恐怕不可能。也就是说，同样的资源对生产小麦，和生产电脑产生了不一样的效果。表现在曲线上，即两条生产可能性曲线的斜率是不一样的。在此，你可以把斜率理解为曲线变化的弯度，或者弧度。对照PPC1和PPC2的图我们就可以理解，因为化肥产生的效用对小麦的影响更大，所以小麦的生产可能性曲线更“弯”一些，即斜率更大。

请你自己结合“机会成本”的概念和我们今天的例子，想想在实际的生产中，如何合理的分配资源。

原文作者在最后列了一张图表，请你从四种资源的分类来分析一下，什么情况下资源会增加？什么情况下资源会减少。

原文如下：

PPC and Resource Changes

来源: 作者Dr. Mary J. McGlasson

The whole societal scenario, where the production possibilities curve (or production possibilities frontier) is fixed, and the choice will be some point on that fixed curve, stems from the original assumption that the resources are fixed.

Just as a quick recap, what are the categories of resources?

Remember, land is any natural resource, labor is any human service, capital (which is not  money) is machinery and equipment, and the last category is entrepreneurial ability, where the entrepreneur is someone who (1) recognizes a profit opportunity, (2) is willing to accept risk, and (3) is able to organize the other resources.

But -- what if the resources aren't fixed?

If resources change, what happens to production possibilities?

The answer, of course, is "it depends."

If there are suddenly more resources, then there is a greater capability to produce, and the PPC moves outward, or shifts to the right.

Now, just to illustrate side point, let me call the two broad categories of output agriculture, like wheat, and manufacturing, like computers.

These categories are often used in production possibilities models because they use resources differently;

agriculture tends to be more labor-intensive, whereas manufacturing tends to be more capital (or machinery) - intensive.

Why does this matter?

Well, I just wanted to point out that underlying resources changes won't necessarily result in a nice, even, parallel shift of the production possibilities.

Consider this: suppose we're producing efficiently, using all of our resources, operating on PPC1.

Then suddenly, someone discovers a fabulous new fertilizer that doubles crop yields.

What happens to the possible agricultural output when you use all of the existing resources, plus you add this fabulous new fertilizer?

You can now produce much more wheat than you could before.

But what happens to the manufacturing output when you use all of the existing resources, and then add fertilizer?

Probably nothing.

So the new PPC (PPC2), does illustrate an expanded ability to produce but it's an uneven shift.

For now though, just to keep things simpler, I'm just going to show even, parallel shifts.

So -- where were we?

OK -- an increase in resources will result in an outward shift of PPC, demonstrating a greater ability to produce.

OK, then what happens if resources decrease?

Fewer resources mean less ability to produce so the production possibilities will shrink, or shift inward.

Now I want you to think about something.

What does it actually mean to say that there is an increase or a decrease in resources?

How does it happen, more specifically, how would a society see more land, more labor, more capital, or more entrepreneurial ability?

In this table, I've gotten you started; now you complete the rest.

继提高心力的10篇文章后，这个阶段我会陆续写经济学的基础概念。三个月的课余时间里我完成了硕士的经济学和金融学课程。好的经济学不是停留在纸面上，而是告诉人们如何不受经济学家的当。

下一个阶段我打算写关于如何高效学习的文章。