Spelling, meaning and semantics

This blog site will help me to keep a record of my learning during a unit I've just started as part of my journey towards a Master's degree.  The unit is on "Guided Inquiry". I was curious about the difference between the words inquiry and enquiry. According to some sources they're interchangeable ... but I prefer the explanation that "enquiry" refers to a question and is a more "informal" word, whereas "inquiry" refers to a more formal investigation.

Photo credit