Principal vs Principle——这是一对“双胞胎”单词，辨析这对双胞胎的难点不仅在于两个单词外形相似，它们的意思也有容易混淆之处，今天我就帮助您把这两个词彻底搞清楚。
Principal，这个词有名词、形容词两个词性，我们先看一下字典中的解释：
Collins：
1. Principal means first in order of importance.
2. The principal of a school, or in Britain the principal of a college, is the person in charge of the school or college.
Webster：
1. most important
2. a person who has controlling authority or is in a leading position
看到这里，您一定明白了，principal
作形容词是“最重要、最主要”“的意思——The principal reason for my change of mind is this. 我改变主意的最重要原因就是这个。
作名词时是”校长、学校话事人“的意思——Donald King is the principal of Dartmouth High School. 唐纳德·金是达特茅斯中学的校长。
Principle，只有名词词性：
合作原则
Collins：
1. A principle is a general belief that you have about the way you should behave, which influences your behavior.
2. Scientific principles are general scientific laws which explain how something happens or works.
3. The principles of a particular theory or philosophy are its basic rules or laws.
Webster：
1. a moral rule or belief that helps you know what is right and wrong and that influences your actions
2. a law or fact of nature that explains how something works or why something happens
3. a basic truth or theory: an idea that forms the basis of something
这个词的名词含义有三项：
1）（人的）行为准则——Buck never allowed himself to be bullied into doing anything that
went against his principles. 巴克从来不让自己被迫做任何违背自己原则的事。
2）（机器等或自然界的）原理，定律——These people lack all understanding of scientific principles. 这些人缺乏对科学原理的全面理解。
3）（事物的）基本原则，基本法则（如会计原则）——a violation of the basic principles of Marxism.…对马克思主义基本原理的一种违背。
另外，Principal 和 Principle两个词的发音完全相同，都是[ˈprɪnsəpl] 。
英语中，像Principal vs Principle这样的单词“双胞胎”还有很多，我会在今后继续为您介绍、辨析。
