Renaissance scholars, such as Giovanni Pico della Mirandola, believed that absolute truth existed and reasoned that the only way to learn it was to study the past and the whole of human knowledge. The great thinkers of the time studied everything from ancient Greek and Roman writings, to the works of pagan, Christian, Jewish and Muslim scholars. This belief in absolute truth began to change in the 16th Century, however, when the writings of an ancient Greek philosopher called Pyrrho became popular. Pyrrho believed that absolute truth did not exist and that nothing could be known for certain. To some extent, this worldview continues to this day.