The scientific study of any aspect of the world uses the scientific method to acquire knowledge. To apply the scientific method, a researcher with a question about how or why something happens will propose a tentative explanation, called a , to explain the phenomenon. For a scientific explanation to be testable, it must also be . Char heard from her friends that marijuana use can cure glaucoma so it should be legal in all 50 states. Char knows that she is biased in favor of marijuana legalization, so she decides to exercise some skepticism about this claim. She researches where her friends got their information, how reliable it is, and what other sources say about legalizing marijuana. Char is . Wilhelm Wundt used (he called it "internal perception"), a process by which someone examines their own conscious experience as objectively as possible, making the human mind like any other aspect of nature that a scientist observed.