What's the difference between 'ask' and 'inquire'? Can I use them interchangeably?

Question

For example, see the following reference:

Denison was interested, went over to him, and watched the swift, skilful manner in which the thin brown fingers worked.

"Where are you going to fish?" he inquired.

The broad, flat face lit up. "Outside in the dam deep water--sixty, eighty fa'am."

Can I also use "he asked" here? Where are the places I cannot use ask instead of inquire?

Answer 1

You can ask that someone perform an action.
When you inquire you only request information.
You can ask for permission, a favour, or forgiveness, but not inquire for them.
They're not interchangeable, ask is broader.

Answer 2

In American and Australian English, they are interchangeable, but an inquiry would be a more formal investigation.

Answer 3

In the most basic form, ask can be applied to any question and the response may be completely ignored if not required. Inquire, on the other hand, implies an eagerness on the part of the former to receive a response.