In looking back over the history of science, we find that some of its greatest innovators have actively promoted empirical knowledge in certain parts of their fields while vigorously defending various concepts which might be referred to as "floating," because they could never contribute to determinate predictive knowledge in other parts of their subject matters. William Harvey, for example, who sought out and organized a vast store of evidence to support the hypothesis of the circulation of the blood, even though he did not observe the capillaries, is said to have defended the theory that various diseases can be explained in terms of the traditional four humors of the body.