  Soft breaking of a symmetry requires an invariance of the dimension-4 part of
the Lagrangian and non-trivial variation of the lower-dimensional part.
However, in general, separation between the dim-4 and lower-dimensional
Lagrangian is not invariant with respect to basis transformations of fields.
Therefore, a natural question of the physical meaning of soft symmetry breaking
arises. This problem is addressed here in the framework of two-Higgs-Doublet
Models (2HDM). It has been shown, within these models, that in spite of the
ambiguity corresponding to the separation between dim-4 and the lower-dimension
Lagrangian, implications of the soft symmetry breaking could be formulated in
terms of observables, i.e., they are physical and measurable. There are six
global symmetries that can be imposed on the scalar sector of the generic 2HDM.
Necessary and sufficient tree-level conditions for soft breaking of all of them
have been formulated in terms of observables.
