By having a look at the situation which is basically the purpose of your letter as well as the audience which is basically to whom you are writing to, you will be able to know which tone as well as context to use so as to enable smooth conversations.
Observe the situation you are in which means the context and the purpose of the letter. The tone used should be adjusted by understand the reason of writing the letter. In terms of content, it should usually be straight to the point and not too wordy or long-winded as it tends to confuse the recipient of the content of the letter.
It is to look and it depends on the purpose you writing to the other person and whom you are writing to
IT is based on the situation that you are in and it is also based on who you are writing to. If the person that you are writing to is of higher authority, then a very polite tone would be the best.
The content should be related to the purpose of your writing. A complaint letter should state the issue or incident you have to complain about. As such, the purpose is closely related to the content. Depending on the addressee, the tone should be adjusted accordingly. Recipients of higher authority have to be courteously addressed. The tone also depends on the severity of the issue, such as a serious tone in complaints and a slightly more light-hearted one when addressing someone over a minor issue.
We decide the tone by knowing what is the purpose and the audience. LIke for example, if you are writing a letter to your teacher, principal or a highe authority,you should be very polite and formal(never be casual). However, if you are writing to your friends or your parents or to someone else whom you may know much better than the others(might be casual).Moreover, you also have to take note of what you are writing.For example, if you are writing to your parents who have gone overseas,asking about their wellbeing, the letter might be casual and informal. However, if you are writing a leave letter to your teacher telling him the teacher why you are late, you have to be very formal(not casual). This is because when you want to write a leave letter to your teacher,you must convince him on the reason why you are late and the main thing is to remember who you are writing to. This is how to determine whT tone to use and what content to include the letter.
Firstly, the sender should review the reason he is writing and what he is writing about. This would then give him an idea on what tone to use and what content to include.
It has to depend on the purpose of writing and the target audience I'm writing to. If I were to write to someone of a higher authority about something important, it should be a formal letter, the register should be formal and the tone should be polite. However, if I were to write to people im close to like my friends or family, it should be a informal letter, the register should be informal and the tone should be comfortable and casual.
It depends on the purpose of the email/letter and the recipient and the relationship with the recipient
I would think about how I would actually talk to the person in real life. If I am writing to my pen pal of 3 years, I would use a more informal tone because I have known him/her for 3 years. If it is to a teacher, I would use a more formal tone as he/she is senior.