We've looked at the impreciseness and ambiguity of natural language statements, but these are not the only problems hidden in natural language arguments. The following illustrates a common form of hidden assumption: saying "the tenth reindeer of Santa Claus is ..." implies the existence some tenth reindeer. More subtly, humans use much more information than what is spoken in a conversation. Even aside from body language, consider a friend asking you "Hey, are you hungry?" While as a formal statement this doesn't have any information, in real life it highly suggests that your friend is hungry.
A much more blatant form of missing information is when the speaker simply chooses to omit it. When arguing for a cause it is standard practice to simply describe its advantages, without any of its disadvantages or alternatives.
ASIDE: Economists measure things not in cost, but opportunity cost, the price of something minus the benefits of what you'd get using the price for something else. E.g., for $117 million the university can build a new research center. But what else could you do on campus with $117m?
Historically, logic and rhetoric, the art of persuasion through language, are closely linked.