關于這兩個詞（組）的區別，我用漢語和英語分別解釋一下，英語解釋更容易理解：

decide 解決;判決;裁決：If you decide something, you choose what something should be like or how a particular problem should be solved. 例如：

You have the right to decide your own future. 你有決定自己未來的權利。

decide on 決定;選定：If you decide on something, you choose it from two or more possibilities. 例如：

Let's go back. We can decide on our next step tomorrow. 我們還是回去，明天再商量別的辦法吧。