[Grammar] reason for why/reason why

Hello everyone,

I have a doubt on the necessity of preposition in the following sentence:

Canadians who responded to the 2010 Census gave various reasons for why they made a donation to charity.

Is the preposition for required here, or should it be removed?

As always, your help would be much appreciated.

I would change the end to "reasons for giving a donation to charity".

LaMelange said:

Is the preposition for required here, or should it be removed?

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I think it should be omitted if followed by a why clause.

Thank you, Mike and Piscean. Your sentences are definitely better.

Matthew Wai said:

I think it should be omitted if followed by a why clause.

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Mathew, that is exactly what I think, but I am not completely sure, and I would like to know that.