The passage discusses the limitations of Classical Mechanics (CM) and introduces the concept of classical and quantum fluids, emphasizing that CM remains valuable despite its insensitivity to atomic structure. It then delves into the introduction of classical field theories, defining them as theories that involve mathematical fields (scalar, vector, tensor, or spinor) and postulating laws with specific invariance properties. The text distinguishes between pure field theories, which do not require a material substrate, and material field theories, which refer to extended material systems. It highlights the philosophical questions surrounding the concept of fields, particularly the justification of fields being unobservable and the operationalist approach to measuring field strengths. The passage argues that field strengths are introduced as primitives and measured indirectly through their effects on test bodies, rather than being defined in mechanical terms.The passage discusses the limitations of Classical Mechanics (CM) and introduces the concept of classical and quantum fluids, emphasizing that CM remains valuable despite its insensitivity to atomic structure. It then delves into the introduction of classical field theories, defining them as theories that involve mathematical fields (scalar, vector, tensor, or spinor) and postulating laws with specific invariance properties. The text distinguishes between pure field theories, which do not require a material substrate, and material field theories, which refer to extended material systems. It highlights the philosophical questions surrounding the concept of fields, particularly the justification of fields being unobservable and the operationalist approach to measuring field strengths. The passage argues that field strengths are introduced as primitives and measured indirectly through their effects on test bodies, rather than being defined in mechanical terms.