What did Herbert Spencer mean by the persistence of force?

Herbert Spencer defined the persistence of force as a fundamental law of matter, which serves as the cornerstone of his synthetic philosophy.1

In his work First Principles, Spencer argued that this law dictates that nothing homogeneous can remain unchanged when acted upon by an external force. Because any such force must affect different parts of a homogeneous entity in varying ways, it inevitably introduces diversity and variety.1

Spencer posited that this process leads to what he termed the "law of the multiplication of effects." He believed that any force continuing to act upon a homogeneous system will produce increasing complexity. For Spencer, this principle—ultimately derived from an unknown and unknowable absolute force—provided the essential key to understanding all development, whether in the cosmic or biological realms.1