Although the terms theory, fact, and hypothesis are sometimes treated as though they had clear meanings and clear relations with one another, their histories and uses are more complex and diverse than might be expected. A fact is usually thought of as a described state of affairs in which the descriptions are true, but how something becomes a fact has been a major concern of sociologists of scientific knowledge. Hypotheses and theories can also be defined as rooted in what is or can be established as fact, which raises difficult questions.