Even in English 'against' can be used similarly. "How is the Euro trading against the Dollar?" Here it wouldn't be used the same (that is, 'I trade my wine against a beer' doesn't make sense), but hopefully that might help a bit.
Yes, 'contre' is 'against' sometimes, but as the suggestions and usage here shows, also 'for' or 'in exchange'.
It's confusing, mais c'est la vie. :-)
Merci, mais expliquez un peu plus, s'il vous plait? Why can't we use "échange" & "pour"?
I suggested "contre" is used with the verb "échanger" as an improvement, according to this article - http://french.about.com/od/grammar/a/preposition_contre.htm.
But the presence of "avoir" meaning to "exchange" here complicates my thinking.
So, my original question - Why specifically can we not use "pour" with "j'échange"?
Merci beaucoup x
That is a good point, but I think DuoLingo should be open to broader translations, as translating is definitely not exact and sayings in one language do not exactly equate sayings or ideas in another. I think maybe DuoLingo should point out some of these subtlties instead of failing someone as it can definitely be an issue of judgement.
Think of echange as meaning exchange and contre as meaning for. As I see it, the French are exchanging against something. Same thing happens with medicines--English says a medicine is for a disease, French says it is against the disease. Prepositions are known for being used differently across languages and even regional speaking patterns.