decide against

1. 作出不利于……的判决

The judge had decided against him.

法官的判决对他不利。

2. 决定不

I decided against leaving.

我决定不离开了。

decide on/upon

1. 考虑后决定

Finally, she decided on a pink dress.

最后, 她选定了一件粉红色的衣服。