How to distinguish between 为 and 给 when both means "for"

Question

Both 给 and 为 can mean "for." Both can be used with verbs to express an action done for anyone.

So how can I distinguish? Please make it clear.

Thank you so much.

Answer 1

My feeling is:

That 给 is for doing something ''for'' someone.

I will buy it for you. 我给你买。

You will do the verb for someone else.

And 为 is more abstract

I am sad for you. 我为你伤心。

I'm not native but I don't think you could say:

我为你买东西。 X

我给你伤心。 X

Answer 2

If you do something 'for someone's sake' or 'on behalf of someone', you can use 给

[给 + noun] = [for + noun (for noun's sake)] e.g. 给我买东西 (buy thing for me = buy thing for my sake)

[给 + noun] = [for + noun (on behalf of noun)] e.g. 给我重重打 (severely beat someone for me = beat someone on my behalf). In this case, 给 is interchangeable with 替 (on behalf of)

If you do something 'for someone's sake', or 'because of someone' you can use 为

[为 + noun] = [for + noun (for noun's sake)] e.g. 为我买东西 (buy thing for me = buy thing for my sake)

[为 + noun] = [because + noun ] e.g. 为我而受苦 (suffering because of me). In this case, 为 is interchangeable with 因 (because of)