Word Choice: Principle vs. Principal

“Principle” and “principal” sound and look very much alike. In addition, neither word is very common in everyday language, so it can be hard to remember what each term means.

However, there is an important difference between these words. Don’t worry, though! You can follow our advice on how to use “principle” and “principal” correctly to make sure your work is error free.

Principle (A Rule or Guiding Idea)

“Principle” is always a noun (i.e., a naming word). Typically, it refers to an idea or rule that explains or controls how something happens. For example:

Time travel would violate the principles of modern science.

Democracy works on the principle of one person, one vote.

The first sentence above refers to established scientific laws. The second refers to a guiding idea.

A similar use of “principle” is to refer to a “moral standard,” such as if we say:

I am kind to animals as a matter of principle.

In addition, sometimes “principle” is used in contrast to practice. For example:

I’m in favor of the new law in principle, but it could cause problems.

Here, saying “in principle” means “in theory” or “as an idea,” but this is contrasted with concerns about how the “principle” will be applied in real life.

Principal (First or Most Important)

“Principal” is most often an adjective (i.e., a word that describes a noun). When used like this, it means “first in order of importance.” For example:

Petroleum is the principal export of Saudi Arabia.

My principal reason for taking the job was the salary.

In these cases, “principal” works as a synonym for “main” or “most important.”

This word can also be a noun, though. When used like this, it usually refers to the person in charge of a school:

The new principal addressed the students at assembly.

The noun form of “principal” also has some less common meanings. As a legal term, for example, it refers to the person directly responsible for a crime. You won’t need to know technical definitions like this to use this term on a day-to-day basis, but it is worth looking out for unusual usages!

Principle or Principal?

With these terms, if you are looking for an adjective, it will always be “principal” that you need. But telling the noun forms of these words apart can be tricky! Our advice is to remember that a “principal” is usually a person, whereas a “principle” is a rule or belief. You should therefore be able to work out the correct term from the context.

Principle = Rule or guiding idea (noun)

Principal = First/most important (adjective) or head of a school (noun)