"Creativity" is a difficult word to define. It means that any action can be more or less creative. Lateral thinking is sometimes used as a synonym for creative thinking or idea discovery, whereas vertical thinking is the refinement and improvement of existing ideas. The world's most famous fictional detective, Sherlock Holmes, often exhibited lateral thinking. Weisberg championed the everyday view of creativity in his analysis of the antecedents of creative thinking. For example, he presented a brief biography of Alexander Calder, a popular artist who is best known for his brightly colored mobiles. It does seem that creative thinking involves the "noticing" or remembering of some critical aspect of the environment or a problem that the rest of us overlooked. Guilford described the relationship between problem solving and creativity this way: Problem-solving and creative thinking are closely related. It is clear that creative thinking is a skill that can be cultivated.