Ban – Bar – Prohibit – Forbid

Ban tends to have a legal significance. Forbid and prohibit are more general, though prohibit is more formal.

When you forbid something, you refuse to allow it. You might have heard your parents say things like, "I forbid you to play ball in the house!" or "I forbid you to have any more parties when we're not home!" 

Forbid comes from the Old English word forbeodan, meaning "forbid, prohibit." Forbid can also mean "prevent" or "keep from happening." The spare tire on your car will forbid you from driving any faster than 40 miles an hour – any faster and the car will shake. You may have heard forbid used in the expression "God forbid . . ." This refers to something you hope will not happen, so much so that you're asking God for a little help. 

If a sign says "Swimming Prohibited," don't go for a dip. It's not allowed. To prohibit is to forbid, or to disallow something. 

In school, you are prohibited from leaving the premises before the end of the school day. The school administration also prohibits smoking and chewing gum. In 1920, it became illegal to sell alcohol in the United States. This time period when alcohol was prohibited is known as the era of Prohibition. Famously Prohibition did not work. When you prohibit something, you often make it seem more appealing. 

The verb to ban means to forbid something from being or happening; the word can also be used as a noun. A school board might put a ban on all books that referred to Jefferson's mistress if they didn't want anyone reading about her. 

If your parents are upset by how much time you spend surfing the net, they might ban all computers in the house. To ban something is to put a ban on it. Something with a ban on it is said to be banned. At the height of the disco craze, radio DJs banned all disco records. To get listeners to join their ban, they encouraged them to destroy their disco records in public.

In their definitions relating to prohibition and exclusion, the verb ban usually applies to things, and bar usually applies to people. For example, you might ban chocolate cake from your house and say that anyone caught sneaking in chocolate cake will be barred indefinitely. We qualify the distinction with “usually,” however, because it is not a rule, and exceptions abound. Meanwhile, the two words are synonyms when applied to actions (so the act of eating chocolate cake might be either banned or barred), which further blurs the distinction.

Ban is often used to denote official actions of governments and other authorities, while barring is more often unofficial. Also, while ban doubles as a noun, bar does not. There are so many other noun senses of bar that using the word as a synonym of prohibition or exclusion might just cause confusion.

In British English, ban and bar are more closely interchangeable than they are in American English.

For example, these writers use ban in relation to things or actions:

A number of suspensions for drinking, fighting and swearing has led Sydney Academy to ban dances next year. [CBC]

Our children’s school has now banned tree climbing. [Telegraph]

Many young adults dislike abortion and are receptive toward pro-life arguments, but feel uncomfortable with banning abortion entirely. [National Review Online]

And these writers use bar in relation to people or actions:

However, a race in South Africa has led to the AAA barring him from the event. [Guardian]

Legislation to bar those convicted of crimes from serving on school boards and requiring board members to undergo criminal checks has been signed into law. [Star-Ledger]

School rector Father Paul Martin has barred Keith from attending because school policy does not allow “old boys”… [Stuff.co.nz]