Since gauge symmetries cannot be spontaneously broken, this calls into question the validity of the Higgs mechanism. In the usual presentation, the Higgs field has a potential that appears to give the Higgs field a non-vanishing vacuum expectation value. However, this is merely a consequence of imposing a gauge fixing, usually the unitary gauge. Any value of the vacuum expectation value can be acquired by an appropriate gauge fixing choice. Calculating the expectation value in a gauge invariant way always gives zero, in agreement with Elitzur's theorem. The Higgs mechanism can however be reformulated entirely in a gauge invariant way in what is known as the Fröhlich–Morchio–Strocchi mechanism which does not involve spontaneous symmetry breaking of any symmetry. For non-abelian gauge groups that have a SU ( 2 ) subgroup, this mechanism agrees with the Higgs mechanism, but for other gauge groups there can appear discrepancies between the two approaches.