1. It's one thing to use a word, it's another to explain it.
     It's one thing to , it's another to .  
2. I went on talking, as if a thousand vague words would add up to one accurate definition.
     , as if add up to . 
3. I had no idea because the longer I thought about idioms the less sure I was what they were.
     the longer the less sure . 
4. I'd been so inspired by the driver's determination to learn English that I didn't fully grasp the potential for linguistic fraud committed in this man's cab.
     so inspired by that .
5. I can only trust that someone as curious as he is also owns a dictionary.
     someone as .