In her language formation talk, Erin McKean encourages us to make up words.
As a lexicographer, McKean tries to include as many words as possible in the dictionary. It is not up to her, however, to decide what is or is not a word. That is a decision that is left up to everyone who speaks a language. McKean notes that a language is really just a group of people who have agreed to understand each other. That being said, there are a lot of people out there who will try and discourage people from making up words on the basis of grammar. McKean frowns upon this, noting that there are two types of grammar; the first of which is the natural, unconscious rules that native (or proficient) speakers of a language follow without thinking. The second grammar, referred to as usage, is more rules-based and, thus, used to discourage.
McKean encourages the creation of language, however, and offers six ways to do so, which range from stealing from other languages to implementing a functional shift in existing words. Each new word we create is a new chance to express ourselves and facilitate more meaningful exchange.