Particles and Non-Particles in Quantum Field Theory

The particle concept is widely used in quantum field theory, yet its applicability is often assumed rather than structurally defined. This paper introduces explicit criteria for particlehood based on identifiability, persistence, and transportability, and applies them within the framework of the Standard Model. It is shown that field quantization alone does not imply the existence of particles, and that several degrees of freedom commonly treated as particles fail to meet these criteria. In particular, gluons and virtual excitations are identified as non-particles in a principled sense, while photons occupy a boundary regime in which particle language is only conditionally valid. The analysis leaves the formalism, symmetries, and predictive success of the Standard Model entirely intact, while clarifying the interpretational limits of particle-based descriptions. By separating computational structures from ontological commitments, the work provides a disciplined reorganization of particle language that resolves longstanding conceptual ambiguities in quantum field theory.