Why does writing well matter? So much of grammar seems arbitrary, annoying, and irrelevant to communication.

The real reason correct and clear writing matters is credibility.

Credibility is how believable someone or something is. We talk about credibility in terms of evaluating sources for research projects or determining whether a particular web page has accurate information or not. When we judge the credibility of people, we evaluate a few factors very quickly.

When we see people, one of our first indicators of credibility is the person's appearance. We notice whether the person is groomed and what clothes the person is wearing. Without thinking about it, we are evaluating whether the choices they have made fit the context and style of the situation. For example, if someone is wearing a suit in an office, they appear credible because their clothing matches the context. And if the suit is attractive, then their level of credibility increases. If the suit is ill-fitting, worn or less than clean, then we make other judgments about the person that would tend to decrease their credibility--they understand the context, but not the style of the situation.

On the other hand, if we are out hiking in the mountains and see someone wearing a suit, we'd probably judge that person as having very little credibility because their clothes do not match the context. Suits are not practical clothing for hiking. If the person looks injured or confused, we might approach and ask if they need help because we could imagine a scenario to explain the odd clothing choice appearing in that context. However, if the person is wearing a suit and carrying a water bottle, we might question the person's sanity.

Credibility has to do with understanding the conventional rules of style and context: what is appropriate when. Appearance is one way to judge whether a person understands these conventions.

Once we meet a person, many other factors come into play: knowledge, education, training, likeability. We begin to evaluate the person's credibility based on further (and probably more reliable) information than just appearance.

This kind of face-to-face evaluation probably seems pretty familiar. Even if we don't think about it, we're used to making these kinds of evaluations every day. But we may not be as used to using written material alone to determine someone's credibility.

The written document works the same as someone's appearance; it indicates whether a person has a working knowledge of the rules and conventions that everyone has already agreed upon. When a person demonstrates an understanding of conventions, that person establishes a baseline credibility. When the person doesn't, then the person has no credibility.

So a grammar mistake in a document is just like a person hiking in a suit; it's a recognizable sign that something isn't quite right and that the person may not know what s/he is doing. Showing that you understand the rules and conventions of not only grammar, but also formatting of documents, indicates that you are a knowledgeable person able to recognize and conform to (when appropriate) the conventions of society. This is what makes you credible.

When you're agonizing about why grammar matters or why people care about word choice and spelling mistakes, keep in mind that these errors are signals of credibility, and you want to represent yourself as best you can in all of your written documents.

And comedy occurs when people contradict, generally without knowing it, social conventions, which is part of why we find things like autocorrected text messages so funny.