  An unsolved problem in turbulent dynamo theory is the ``back reaction''
problem: to what degree does the mean magnetic field suppress the turbulent
dynamo coefficients which are needed to drive its growth? The answer will
ultimately derive from a combination of numerical and analytical studies. Here
we show that analytic approaches to the dynamo and back reaction problems
require one to separate turbulent quantities into two components: those
influenced by the mean field (which are therefore anisotropic) and those
independent of the mean field (and are therefore isotropic), no matter how weak
the mean field is. Upon revising the standard formalism to meet this
requirement, we find that: (1) The two types of components often appear in the
same equation, so that standard treatments, which do not distinguish between
them, are ambiguous. (2) The usual first-order smoothing approximation that is
necessary to make progress in the standard treatment is unnecessary when the
distinction is made. (3) In contrast to previous suggestions, the correction to
the dynamo $\a$ coefficient found by Pouquet et al (1976) is actually
independent of the mean field, and therefore cannot be interpreted as a
quenching.
