  We propose a new theoretical and practical framework for the study of
light-matter interactions and the angular momentum of light. Our proposal is
based on helicity, total angular momentum, and the use of symmetries. We
compare the new framework to the current treatment, which is based on
separately considering spin angular momentum and orbital angular momentum and
using the transfer between the two in physical explanations. In our proposal,
the fundamental problem of spin and orbital angular momentum separability is
avoided, predictions are made based on the symmetries of the systems, and the
practical application of the concepts is straightforward. Finally, the
framework is used to show that the concept of spin to orbit transfer applied to
focusing and scattering is masking two completely different physical phenomena
related to the breaking of different fundamental symmetries: transverse
translational symmetry in focusing and electromagnetic duality symmetry in
scattering.
