§ 25. In order for a relationship between appearances to be valid as an objective experience, it must be formulated in accordance with an "a priori" concept. The concepts of substance/accident, cause/effect, and action/reaction (community) constitute "a priori" principles that turn subjective appearances into objective experiences. The concept of substance relates appearances to existence. The concepts of cause and community relate appearances to other appearances. The principles that are made of these concepts are the real, dynamical [ Newtonian ] laws of nature.