At the smallest level, lexical items--or words--contribute to the tone of a piece of writing. Although two words might convey similar meaning (denotational meaning), one may only be used formally, while the other informally (connotational meaning). For example, the verbs "to dine" and "to eat" convey an intake of food--denotatively. However, if you think about these two words, you'll find that the former is usually used formally, while the latter usually informally. Therefore, when you use these words in your writing, your writing will appear formal to the reader. On the other hand, other words are usually used informally, and using these words, you will make your writing sound informal as a result. Expressions such as "big deal," "stuff," or "freak out" are used more in informal, spoken conversations, thus transmitting informal tones.
Informal diction includes slang, colloquialisms as well. We advise you to consider the context when making a decision as to what lexical items you will use. This is because although lexical items can connote certain sense of tone, they must be used in an appropriate context as well. For example, it might be a little bit out of place to use the word "to dine" above in the following context: "Last night I dined on pizza with my girlfriend." This is because "to dine" is usually found to be used with exquisite dishes like coq-au-vin, or foie gras, rather than with pizza, which one usually eats with his or her hand. So as a writer not only do you have to choose the words that sound formal or informal, but you must also determine whether the context is appropriate for those words as well.
Contractions or AbbreviationsIn colloquial or informal speech, language users usually clip or shorten words or expressions, which might be due to ease of pronunciation or phonological factors. So, contractions such as "aren't," "isn't," "wasn't," and "haven't" (as opposed to "are not," "is not," "was not," and "have not") are thought of as belonging to informal spoken speech rather than formal written speech.
Included in the category of contractions is omission of "connectors" such as "that" in "He says (that)" "The author argues (that) Shakespeare. . ." or "The weather is so hot (that) I went to have a swim." The connector "that" is usually omitted in casual speech, but in formal writing "that" should be retained.
Point of ViewIn writing, you have to decide who is going to tell the story (or make an argument, etc), who is going to listen to the story, and the relationship between them. Such a relationship is like the angles of a camera in film making, and it is very important because it will affect the overall meaning of what you're writing. One grammatical way to establish that relationship is to use pronouns: first-, second-, or third persons, singular or plural, pronouns. Click here for more information about pronoun use.
For example, if you imagine the relationship between yourself (i.e. the writer) and the reader to be that of a friendly conversation, you can use the first-person (singular or plural) to call yourself ("I" or "We"), and the second person (singular and plural) to address the reader ("you" or "you guys"). This strategy is usually found in advertisements where the ad makers wish to appear to be friendly and informal (hence be able to sell their products). Notice that this grammar webpage also uses "we" and "you" so as to appear user-friendly.
On the other hand, if you want to be formal, we advise you to use third person (singular and plural), and sometimes you might hear that this strategy is called "impersonal." This strategy is much used in scientific writings or formal paper writing because one of the purposes of sciences--as you might know--is to be objective, and thus it does not matter, for example, who does an experiment ("I" or other people), and the results of the experiment should be the same regardless of who does the experiment. Perhaps because using first persons can make your writing more subjective, your writing instructors caution you against the use of "I" and "we" or against addressing the reader with "you." However, because we think that each piece of writing has its own purposes and own audiences, and that not every writing should appear to be objective and formal, we leave with you the decision to choose the point of view from which to write your paper.