= Causal Dirac spinor current
{title2=$V^0=\epsilon^\dagger\epsilon,\quad V^2\le0$}
For a commuting spinor in mostly-plus signature, orient its <Dirac current> to the future and write $V^i=\epsilon^\dagger\alpha^i\epsilon$, with Hermitian $\alpha^i=-\gamma^0\gamma^i$. For every spatial <unit vector> $u$, $(u\cdot\alpha)^2=1$ implies $|u\cdot V|\le\epsilon^\dagger\epsilon=V^0$. Choosing $u$ along the spatial current proves $V^2\le0$. Thus spinor bilinears supply causal <vectors> suitable for energy-condition estimates. A Grassmann-valued spinor does not have this ordinary positivity interpretation.
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