More than just semantics: Words signal relationships.
Many people with social challenges feel more comfortable reading books than interacting with others; as a result, they may have a fantastic vocabulary, but have not learned to vary their speech based on the situation, and so are not aware of the social signals that they are sending via their word choices.
As discussed in the power & solidarity module, formal language distances you from other people, sending the message that you do not wish to interact on a personal level, while using informal language is an appeal to solidarity. If you have been having trouble connecting with people, we recommend that you try to introduce some more informality into your speech, both in your word choices and in your pronunciations (sounds). This does not mean that you “talk down” to people or assume that they are any less intelligent than you – it is simply a recognizable signal that you are being friendly.
The key to successful interaction (as usual) is monitoring those around you. If you are interacting with friends and/or equals, your level of formality should match (mirror) theirs, and perhaps be proactively less formal, to try to encourage a closer relationship.
If you are interacting with someone who has power over you, and your language use is significantly less formal than theirs, you may seem disrespectful, assuming too much familiarity, challenging their authority. But if they become progressively less formal, you should interpret this as a sign of growing closeness, and reciprocate! (If you do not, you may find that they interpret your continued formality as a sign that you do not wish to be close, and so progressively become more formal again.)
If you are interacting with someone subordinate to you (e.g., your employee or your student), they will likely be quite formal with you at first, to show proper deference, but if you continue to sound very formal in return, they will assume that you do not wish to be friendly. (They might think it’s up to you, the superior, to initiate a more friendly relationship.)
Formal vs. Informal Vocabulary
Just about every major publisher has some kind of “writer’s manual” or “usage manual” that discusses the issue of word choice. Most of them are simply prescriptive, telling you what informal words and phrases to avoid in formal, academic writing. Most take an encyclopedic approach, listing page after page of vocabulary items, and we have not attempted to reduplicate their efforts here. Rather, we seek to try to explain the distinctions, how they are perceived, and the social consequences of those perceptions. NOTE that “informal” is not the same as “slang” or taboo (“bad”) language (for more about both of which, see below).