Allow, Permit e Let — Diferenças e Usos Gramaticais

These words have [essas palavras têm] similar meanings and uses [usos e significados similares]. Permit is more formal [Permit é mais formal].

Both words can be [Ambas as palavras podem ser] followed by object + infinitive [seguidas por objeto + infinitivo]

• We do not allow/permit people to smoke in the kitchen.

When there is no personal object [Quando não há nenhum objeto pessoal], an -ing form is used. [uma forma com -ing é usada]

• We do not allow/permit smoking in the kitchen.

Passive structures are common [As estruturas passivas são comuns]; personal subjects [sujeitos pessoais] and gerund (-ing form) are both possible. [e gerúndio (a forma com -ing) são possíveis]

• People are not allowed/permitted to smoke in the kitchen.
• Smoking is not allowed/permitted smoking in the kitchen.

The passive structure with it [A strutura passiva com it] is only possible with permit [é apenas possível com permit].

• It is not permitted to smoke in the kitchen. (It is not allowed to smoke in the kitchen.)

Let is the least formal [Let é o menos formal] of these three words [dessas três palavras], and is followed by [e é seguida por] object + infinitive without to [objeto + infinitivo sem o to]. Compare:

• Please allow me to buy you a drink. (Polite and formal)
• Let me buy you a drink. (Friendly and informal)

Let is not usually used in passive. [Let normalmente não é usado no passivo]

• I wasn’t allowed to pay for the drinks. (NOT I wasn’t let…)

Let can be used with adverb particles; passives are possible. [Let pode ser usado com particulas adverbiais; os passivos são possíveis]

• She wouldn’t let me in.
• I’ve been let down.

Fonte: Oxford Practical English Usage, Second. Edition, pg. 36-37.