  We discuss a method to study free protons and neutrons using $\nu(\bar
\nu)$-hydrogen (H) Charged Current (CC) inelastic interactions, together with
various precision tests of the isospin (charge) symmetry using $\nu$ and $\bar
\nu$ CC interactions on both H and nuclear targets. Probing free nucleons with
(anti)neutrinos provides information about their partonic structure, as well as
a crucial input for the modeling of $\nu(\bar\nu)$-nucleus (A) interactions.
Such measurements can also represent a tool to address some of the limitations
of accelerator-based neutrino scattering experiments on nuclear targets,
originating from the combined effect of the unknown (anti)neutrino energy and
of the nuclear smearing. We also discuss a method to impose constraints on
nuclear effects and calibrate the (anti)neutrino energy scale in $\nu(\bar
\nu)$-A interactions, which are two outstanding systematic uncertainties
affecting present and future long-baseline neutrino experiments.
