Thanks for all the replies, I found the discussion very interesting. Cheers.

If anyone is interested, a quick way to check your understanding of the subject is to tell the difference in meaning between these two sentences.

１．　ハワイへ行くとき、くつを買った。

２．　ハワイへ行ったとき、くつを買った。

くつ = shoes
買（か）った = bought

1. When I was going to hawaii I bought shoes.
2. When I went to hawaii I bought shoes.

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You have never disappointed me since you started studying Japanese!! :)