Are pledges tax deductable?

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I know that when you give a donation you can get a tax receipt and the governemnt will reimburse you so much, etc, etc. But is it the same if someone pledges you? Im doing a walk-a-thon and when my teachjer pledged me he asked if he's able to do this. I dont think so but then again it is almost like a donation...but not really. Anyone know the true answer to this? Specifically in Canada?