Bound Nucleon Structure in QCD and Quark Confinement*

The reasons for believing that nucleons that are bound in nuclei are different from those that move freely are discussed using examples from experiment and theory. These show that the structure of the nucleon must be modified by its presence in a nucleus, and that  the modifications must be small. Existing data regarding lepton-nucleus interactions and simple theory based on  electromagnetic current conservation and analytic properties of scattering amplitudes are used to display the importance of quark confinement in limiting the sizes of some of these modifications. Furthermore, quark confinement is shown to be an essential requirement in understanding   lepton-nucleus interactions and  the resulting derived nuclear properties to be as they are observed.