Forbidden vs Illegal vs It's against the law

When to use each in English, with meaning, register, and examples.

Forbidden

FormalTop 3,000 (common)

Illegal

FormalTop 2,000 (common)B1adjective

It's against the law

FormalTop 5,000 (fairly common)
Most common: Illegal
 ForbiddenIllegalIt's against the law
Pronunciation🇬🇧 //fəˈbɪd.ən//🇺🇸 //fərˈbɪd.ən//🇬🇧 //ɪˈliːɡ(ə)l//🇺🇸 //ɪˈlɪɡəl//🇬🇧 //ɪts əˈɡeɪnst ðə lɔː//🇺🇸 //ɪts əˈɡeɪnst ðə lɔ//
MeaningNot allowed or banned.Not allowed by law.It is illegal.
ExampleThe secret room was strictly forbidden to anyone except the owner.Driving without a license is considered illegal.Driving without a license is really {{highlight}}against the law{{highlight}}.
RegisterFormalFormalFormal
How commonTop 3,000 (common)Top 2,000 (common)Top 5,000 (fairly common)
CEFR level-B1-
Part of speechadjective
Collocationsforbidden zone, forbidden love, forbidden activities, forbidden fruit, forbidden cityillegal activity, illegal immigration, illegal drugs, illegal parkingagainst the rules, against the regulations, against public policy
Antonymsallowed, permitted, legallegal, permissible, lawfulit's legal, it's allowed
Common mistakesConfused with 'prohibited' - both mean similar things, but 'forbidden' is less formal., Incorrectly used as a verb - 'forbidden' is strictly an adjective., Using 'forbidden' in positive contexts - it always suggests something disallowed.Confused with 'unlawful', which can have a broader meaning., Using 'illegal' to describe moral wrongs instead of legal ones., Misusing as a noun instead of an adjective, e.g., saying 'the illegal is punishable' instead of 'the act is illegal'.Confusing with 'it's legal' meaning allowed., Using with informal language., Misusing in non-legal contexts.
Usage notesUsed to describe something that is legally or socially unacceptable. Avoid using in casual conversations.Use 'illegal' in formal contexts, especially legal discussions, but also in general conversation. It's not appropriate for casual slang.Use this phrase in legal contexts or when discussing rules. It's formal and not suited for casual conversations.

See it in real clips

Forbidden
Illegal
It's against the law

Frequently asked questions: Forbidden vs Illegal vs It's against the law

What's the difference between Forbidden, Illegal, and It's against the law?

Forbidden: Not allowed or banned. Illegal: Not allowed by law. It's against the law: It is illegal.

Which is more common: Forbidden, Illegal, and It's against the law?

Illegal is the most common in everyday English.

Can you show an example of each?

Forbidden: The secret room was strictly forbidden to anyone except the owner. Illegal: Driving without a license is considered illegal. It's against the law: Driving without a license is really {{highlight}}against the law{{highlight}}.

Can I use Forbidden, Illegal, and It's against the law interchangeably?

Not always. Forbidden, Illegal, and It's against the law are related and overlap in some contexts, but they differ in register, how common they are, and usage, so swapping one for another can change the meaning or tone. Check the differences above before substituting.