While can only be used in an action. So any negation requires a different word (if / when / etc) e.g. - While walking down the street, I noticed an accident -> You are literally walking down the street e.g. - When walking down the street, I listen to music. -> You are describing an usual action / a habit (in this situation!) e.g. - If I'm walking down the street, I watch my step -> It connects both sentences, but describes a conditional habit. (Only then, when you walk down the street, if you do so, you watch your step) To answer in short: - While - active conditional used for events during an action - When - consequential conditional used for directly connected actions. - If - direct conditional used for dependent actions

In this case, you can't really use "while" because it can only be used with an action that lasts for a period of time. "If" would be best but you can say "when" too. So, "while" is used with "an action that lasts for a period of time" e.g. swim, run, work..... "when" - "an action that finishes very quickly" e.g. turn off the light, close the door, jump off the cliff (HAHA!)

The word that comes out of my head most naturally is "if". "While" is strange (we use it mainly for real actions), but "when" would be OK. But "if" is definitely the best, for me.

Thank you! I understand. But I have another question related to this. Which of these sentences sound natural? And what's the difference? 1. "He visited the office while I was out." ("being out" isn't an action, but I remember I saw a sentence like this somewhere) 2. "He visited the office when I was out" 3. "I lived in Paris while I was a child." 4. "I lived in Paris when I was a child." (My grammar books say this is correct)