The natural sciences (physics, astronomy, chemistry, biology, and geology) developed out of philosophical speculations about the nature of reality. However, it wasn’t till the late nineteenth century that a systematic study of human thought emerged. One reason for this was that humans could not directly observe the thoughts of others, so philosophers had no basis for understanding how those around them were thinking. Another reason was that they couldn’t test hypotheses about the workings of the mind scientifically because they didn’t possess direct knowledge of brain activity and objectivity in its hypothesis.
In addition, the strictly physical study (although objectively scientific) of the brain – although very important – did not tell us much about how we think and act. Some physiologists, especially in Germany, turned their attention towards studying the brain – and at the same time, philosophers (mainly in the US) took a more rigorous approach to the study of the mind. This led to the birth of a new science called “psychology”, which was able to bridge the gap between philosophy and biology.