When writing a letter, or other form of written work, what is the appropriate way to put emphasis on a word or phrase?
When would one use bold?
When would one use italics?
When would one use an underline?
Do they all mean the same, and their usage is simply a matter of preference?
Edit
I would like to know the definition for each of the above, and why you would use one over the other, specifically in writing a letter or other such document.
For example:
This question is not a duplicate.
This question is not a duplicate.
This question is not a duplicate. (I can't use the HTML tag for underline in HTML 5...)
