What is the difference between "when" and "if"?

[Gella]

English Error, Elementary Level

ESL/EFL Test #12 "At the Finance Company Again", question 9

He offered to share the money with me when I agreed to open a private bank account for him.

(a) offered
(b) when
(c) him

English Error, Elementary Level

ESL/EFL Test #12 "At the Finance Company Again", answer 9

He offered to share the money with me if I agreed to open a private bank account for him.

Correct entry: if
The error was: (b) when
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i'm not sure about 'when'

Gella

[Alan]

Hi Gella,

If is related to a condition and when is related to a time.

When you go on your holiday, send me a postcard - this means at that time.

If you go on holiday, send me a post card - this means you will possibly go on holiday and in that case send me a postcard and so - no holiday = no postcard.

Alan
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English as a Second Language
You can read my ESL story Word Story: Health