Let's examine part of Arnold's post.
For a text message to a friend, I would not use a very formal tone at all. I am familiar with my friends, and they do not require me to follow a specific format for writing. My message would be short, friendly, and maybe funny.
Create one post in response to the following prompt:
Consider the following writing situations: a text message to a friend, a letter applying for a job, and an e-mail to a family member. What is the appropriate level of formality for each situation? How does using an inappropriate level of formality affect communication and the impression it makes?