  A close association between eruptive prominences and CMEs, both slow and fast
CMEs, was reported in many studies. Sometimes it is possible to follow the
material motion starting from the prominence (filament) activation to the CME
in the high corona. Remnants of the prominence were found in the bright core of
CMEs. However, detailed comparisons of the two phenomena reveal problems in
explaining CMEs as a continuation of filament eruptions in the upper corona.
For example, the heliolatitudes of the disappeared filaments and subsequent
coronal ejections sometimes differ by tens of degrees. In order to clear up the
problems of EP-CME association we tentatively analyse the more general question
of the dynamics of a magnetic flux rope. Prominences and filaments are the best
tracers of the flux ropes in the corona long before the beginning of the
eruption. A twisted flux rope is held by the tension of field lines of
photospheric sources until parameters of the system reach critical values and a
catastrophe happens. We suggest that the associated flux rope height above the
photosphere is one of these parameters and it is revealed by the height of the
filament. 80 filaments were analysed and we found that eruptive prominences
were near the so-called limit of stability a few days before their eruptions.
We suggest that a comparison of the real heights of prominences with the
calculated critical heights from magnetograms could be systematically used to
predict filament eruptions and the corresponding CMEs.
