Not all textbooks on quantum field theory necessarily start with a detailed exposition of classical mechanics. While classical mechanics provides a foundation for understanding certain concepts and mathematical tools used in quantum field theory, different textbooks may have varying approaches and prerequisites.
Some textbooks on quantum field theory do begin with a review of classical mechanics to establish a common language and framework. This review may cover topics such as Newtonian mechanics, Lagrangian and Hamiltonian formalisms, symmetries, and canonical quantization. It helps to bridge the gap between classical physics and the more advanced concepts of quantum field theory.
However, there are also textbooks that assume a basic familiarity with classical mechanics and focus primarily on quantum field theory itself. These texts often start with a brief recap of relevant classical mechanics concepts as needed, but they tend to dive into the specific principles, methods, and techniques of quantum field theory more directly.
The choice of whether to include a comprehensive treatment of classical mechanics at the beginning of a quantum field theory textbook depends on the author's intended audience and the level of assumed background knowledge. Some introductory texts target students with a limited background in classical mechanics, while more advanced texts may assume a solid foundation in classical mechanics and delve into quantum field theory more quickly.
It is always recommended to review the table of contents or preface of a specific textbook to understand its approach and determine if it aligns with your goals and background knowledge.