The reflex chain hypothesis was developed to explain the observation that successive movements could be linked together into a contiguous sequence. From the established principles of reflex physiology and association psychology, scientists in the last half of the 19th century began to develop the notion that each of a series of movements may be linked through the sensory results of prior movements. In addition, the same basic principles were applied to mental actions, thus providing a credible explanation for all behavior. The wide applicability of this hpothesis made it an important influence on the scientific thought in the early 20th century.