It is determined by the audience in which we are writing to, as different audiences call for different tones and content to be used. For example, we would use a very friendly tone with friends but not with teachers.
We can determine it by the audience whom we are writing to.
I determine what tone and context to include by whom I am writing the letter to. For example, if I am writing to someone who is of a higher authority, I would use a formal tone.
It would be determined by the purpose and audience of the letter. If the purpose was to ask for a change of CCA from a CCA-in-charge, one should not be demanding.
I can be determined by the whom the audience is and the reason or purpose of the letter.
It can be determined by using Purpose and Audience. Purpose: Why are you writing the letter. Audience: Who you are writing to. For example, the tone and content to be included in a letter/email would be different when writing to the employer for job interview and to a friend to catch up with him.
We can determine what tone to use by knowing who is it and why. We need to know who we are writing to because they might be in higher authority so we should use a respectful tone instead of a informal one. We need to know why we are writing so that use the different tones for various kind of reasons.
You determine the tone of the letter and the content to use by knowing your audience and the purpose. If you are applying for a job, you are writing to a person of higher position then you are and is unfamiliar to you. So the tone should be formal. You should not put emoticons.
You can determine it by the audience and the purpose, using a more formal tone when writing to a superior or a person whom you do not know while using an informal tone when writing to someone close to you.
I can determine what tone to use and what content to write in by keeping in check who the audience and what the purpose is. The abbreviation, PACC(Purpose, Audience, Context and Content) is something containing pointers which helps us stay on track to know what to write when writing a letter. These four pointers are "interconnected" and depend on each other to give the ultimate outcome- the letter. So you will need to know who your audience and what your purpose is to produce a proper letter with the correct tone and the correct content.