We use how come in place of why in a conversation. Here are some examples:
- George: I can’t go to Elaine’s party tomorrow.
- Jerry: How come?
- George: Because I have to work late.
Here’s another example:
- Dan: Would you like some more coffee?
- Jenny: No thanks. I’m trying to cut down.
- Dan: How come?
- Jenny: Because my doctor said too much coffee is not good for my stomach.
We also use how come in place of why in a question. The English grammar for a usual why question is Why + is/are/do/does (etc) + subject + verb/object. The grammar pattern with how come is easy. Just use how come + sentence. Have a look at these examples:
- Why is George late?
- How come George is late?
- Why did Jack miss the party?
- How come Jack missed the party?
- Why are you going there?
- How come you are going there?