This chapter finds that scientific theory is a multiplex structure of polyphasic systems proliferating as a dialectical scale of forms. The concrete, polyphasic unity, which is scientific knowledge, is the integral combination of observation and theory as a dynamic whole an experience. What is required of a theory is coherence and what will coherently systematize the area of experience under scrutiny is the simplest theory. The electromagnetic theory of matter put forward by Lorentz and Larmor explained very coherently the Fitz Gerald contraction, a hypothesis convenient in its turn as an explanation of the null result obtained in the Michelson Morley experiment. While the dialectical progression is apparent even in the relatively limited episodes of scientific discovery, the more general progress is from one dominant conceptual system to another, and each of these constitutes an entire world view implying a metaphysical system.