For + V-ing 是用來表示東西或物品的用途 (purpose or function)。例如：
- There are two knives on the table. One is for cutting fruit and vegetables and the other is just for slicing meat. (桌子上有兩把刀。一把是用來切水果和蔬菜，而另一把只用來切肉) (正)
- What are these two PCs for? (這兩部個人電腦做什麼用 － 用途為何？)
One is for storing vital files and the other is for developing applications. (一部用來儲存重要檔案，另一部用來開發應用程式) (正)
For + V-ing 亦可表示某事發生的原因。例如：
- His father couldn’t talk for coughing. (他的父親咳得說不出話來) (正)
- Helen was famous for singing the hip-hop songs. (海倫以演唱嘻哈歌曲聞名) (正)
To + 不定詞是用來表示動作的目的 (purpose or intention) － 不可用 for + V-ing 來表示動作的目的。例如：
- Professor Chen has gone to Kaohsiung to attend a seminar and to meet some old friends of his. (陳教授已經去高雄參加座談會並和他的一些老朋友會面) (正)
Professor Chen has gone to Kaohsiung for attending a seminar and for meeting some old friends of his. (誤) - George trained to be an accountant. (喬治接受訓練成為一名會計師) (正)
George trained for being an accountant. (誤) - I’m going to Tokyo to visit my uncle. (我將去東京探望我的叔叔) (正)
I’m going to Tokyo for visiting my uncle. (誤) - You don’t need to bring anything. There’ll be food to eat and juice to drink. (你不必帶任何東西來。屆時會有食物可以吃、有飲料可以喝) (正)
You don’t need to bring anything. There’ll be food for eating and juice for drinking. (誤)