  Starting from lagrangian field theory and the variational principle, we show
that duality in equations of motion can also be obtained by introducing
explicit spacetime dependence of the lagrangian. Poincare invariance is
achieved precisely when the duality conditions are satisfied in a particular
way. The same analysis and criteria are valid for both abelian and nonabelian
dualities. We illustrate how (1)Dirac string solution (2)Dirac quantisation
condition (3)t'Hooft-Polyakov monopole solutions and (4)a procedure emerges for
obtaining {\it new} classical solutions of Yang-Mills (Y-M) theory. Moreover,
these results occur in a way that is strongly reminiscent of the {\it
holographic principle}.
