sentences:  The remaining part of the 21st century and longer-term trends are researched by futures studies, an approach that uses various models and several methods (such as "forecasting" and "backcasting").Ever since the invention of history, people have searched for "lessons" that might be drawn from its study, on the principle that to understand the past is potentially to control the future.A famous quote by George Santayana has it that "Those who cannot remember the past are condemned to repeat it."