A critical inspection of quantum field theory will reveal that quantum field theory can be reconstructed only by means of classical field theory. In detail the following six assertions are claimed and proved: (1) Perturbation theory can be achieved by means of classical field theory. (2) Particles that are independent of one another are not correlated. This is especially true for the ingoing particles of scattering processes. (3) Outgoing particles in scattering processes are correlated. But the usual justification of quantum statistics is faulty. (4) In quantum field theory there is an amazing multitude of particle concepts. But a concise description of real existing elementary particles is lacking. (5) The path integral representation is not clearly defined in the particle picture of quantum mechanics. In the wave picture it is only another description of the expansion of a quantum state. (6) Functional representation is nothing else than a comprehensive version of perturbation theory.