It’s easy to get confused with inquire and enquire. They both mean the same thing: to seek information about something or to conduct a formal investigation. But which is which?
Inquire within
The difference between these two is particularly hard to distinguish. According to the Oxford English Dictionary, ‘enquire’ is “to be used for general senses of ‘ask’”. ‘Inquire’, however, is used for when the meaning is more “to make a formal investigation”. The dictionary experts also note that enquire is more common in British English, whilst inquire is more commonly seen in American English. However, a notable exception in British English is that a formal investigation (e.g. by the police) is always an inquiry.

It’s no wonder then that this sign niggled at me. I saw it in Melbourne, Australia, where British English is more common than American. According to the rules above though, they were technically correct!

And some further examples?

You may enquire about a person’s health.
I inquired about the incident last night.

Inquire/enquire can also be a noun – inquiry or enquiry. Thus:

The police were conducting an inquiry.
My friend made an enquiry about my health.