  The minimal coupling method proved to yield definite and correct physical
predictions when applied to fundamental fermions within the framework of
Yang--Mills theories of Standard Model. Similarly, the possibility of
formulating gravity as the Poincar\'e gauge theory gives the opportunity to
produce definite predictions for fermions in the presence of gravitational
field. The minimal coupling procedure, however, cannot be applied naively but
rather needs to be modified slightly such that it is unambiguous. Application
of the corrected coupling method to fermions, together with the inclusion of
the Holst term in the gravitational part of the action, leads to the conclusion
that the Immirzi parameter is in principle classically measurable, in agreement
with the result of Perez and Rovelli.
