Forbidden vs Illegal vs Unauthorized

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

Forbidden

FormalTop 3,000 (common)

Illegal

FormalTop 2,000 (common)B1adjective

Unauthorized

FormalTop 2,000 (common)
 ForbiddenIllegalUnauthorized
Pronunciation🇬🇧 //fəˈbɪd.ən//🇺🇸 //fərˈbɪd.ən//🇬🇧 //ɪˈliːɡ(ə)l//🇺🇸 //ɪˈlɪɡəl//🇬🇧 //ˌʌnɔːθəˈraɪzd//🇺🇸 //ˌʌnəˈθɔərəɪzd//
MeaningNot allowed or banned.Not allowed by law.Not having permission or approval.
ExampleThe secret room was strictly forbidden to anyone except the owner.Driving without a license is considered illegal.He accessed the database without permission, so his actions were unauthorized.
RegisterFormalFormalFormal
How commonTop 3,000 (common)Top 2,000 (common)Top 2,000 (common)
CEFR level-B1-
Part of speechadjective
Collocationsforbidden zone, forbidden love, forbidden activities, forbidden fruit, forbidden cityillegal activity, illegal immigration, illegal drugs, illegal parkingunauthorized access, unauthorized use, unauthorized disclosure, unauthorized personnel, unauthorized transactions
Antonymsallowed, permitted, legallegal, permissible, lawfulauthorized, permitted, sanctioned
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 'unauthorized' and 'unapproved'., Using it to describe actions that are just socially unacceptable., Assuming it can be used in informal 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 term in formal contexts, especially in legal or security discussions. It's not appropriate for casual conversation.

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Forbidden
Illegal
Unauthorized

Frequently asked questions: Forbidden vs Illegal vs Unauthorized

What's the difference between Forbidden, Illegal, and Unauthorized?

Forbidden: Not allowed or banned. Illegal: Not allowed by law. Unauthorized: Not having permission or approval.

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. Unauthorized: He accessed the database without permission, so his actions were unauthorized.

Can I use Forbidden, Illegal, and Unauthorized interchangeably?

Not always. Forbidden, Illegal, and Unauthorized 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.