Written byFizza Butool ZaidiIELTS teacher for 10+ years, PTE for 5Updated 30 October 2026
IDP's formal and informal pairs
From IDP's guide to General Training Writing Task 1 (IDP):
| Formal | Informal |
|---|---|
| request | ask |
| purchase | buy |
| could | can |
| would | will |
| at your earliest convenience | when you are free |
| respond | write back / reply |
| cannot | can't |
| furthermore | and / also |
| Yours sincerely / Yours faithfully | Best wishes / Love |
Sentence style, not just words
IDP says a formal letter has longer sentences with passive language and modals, while an informal letter is conversational and can include contractions and more direct speech (IDP). IDP's formal letter guide adds swaps such as purchased for bought and discover for find out (IDP Australia).
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Match the words to the reader
More formal is not always better. IDP warns that being too formal in a letter to a friend affects your marks, just as being too casual in a formal one does (IDP Australia). Lexical Resource also checks the appropriacy of your vocabulary for the task (key assessment criteria).
Frequently asked questions
Will formal vocabulary raise my band in an informal letter?+
No. IDP says being too formal in a letter to a friend affects your marks.
Is 'could' more polite than 'can'?+
IDP lists 'could' as the formal choice and 'can' as the informal one.
Can I use phrasal verbs like 'find out' in a formal letter?+
IDP's formal sample replaces 'find out' with 'discover', so prefer the single formal word.
Is vocabulary marked separately from tone?+
Tone is part of Task Achievement; Lexical Resource checks the range and appropriacy of your vocabulary. Both are affected.
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