  A clear understanding of the nature of the pre-eruptive magnetic field
configurations of Coronal Mass Ejections (CMEs) is required for understanding
and eventually predicting solar eruptions. Only two, but seemingly disparate,
magnetic configurations are considered viable; namely, sheared magnetic arcades
(SMA) and magnetic flux ropes (MFR). They can form via three physical
mechanisms (flux emergence, flux cancellation, helicity condensation) . Whether
the CME culprit is an SMA or an MFR, however, has been strongly debated for
thirty years. We formed an International Space Science Institute (ISSI) team to
address and resolve this issue and report the outcome here. We review the
status of the field across modeling and observations, identify the open and
closed issues, compile lists of SMA and MFR observables to be tested against
observations and outline research activities to close the gaps in our current
understanding. We propose that the combination of multi-viewpoint multi-thermal
coronal observations and multi-height vector magnetic field measurements is the
optimal approach for resolving the issue conclusively. We demonstrate the
approach using MHD simulations and synthetic coronal images.
  Our key conclusion is that the differentiation of pre-eruptive configurations
in terms of SMAs and MFRs seems artificial. Both observations and modeling can
be made consistent if the pre-eruptive configuration exists in a hybrid state
that is continuously evolving from an SMA to an MFR. Thus, the 'dominant'
nature of a given configuration will largely depend on its evolutionary stage
(SMA-like early-on, MFR-like near the eruption).
