  Filament eruptions often lead to coronal mass ejections (CMEs), which can
affect critical technological systems in space and on the ground when they
interact with the geo-magnetosphere in high speeds. Therefore, it is an
important issue to investigate the acceleration mechanisms of CMEs in
solar/space physics. Based on observations and simulations, the resistive
magnetic reconnection and the ideal instability of magnetic flux rope have been
proposed to accelerate CMEs. However, it remains elusive whether both of them
play a comparable role during a particular eruption. It has been extremely
difficult to separate their contributions as they often work in a close time
sequence during one fast acceleration phase. Here we report an intriguing
filament eruption event, which shows two apparently separated fast acceleration
phases and provides us an excellent opportunity to address the issue. Through
analyzing the correlations between velocity (acceleration) and soft (hard)
X-ray profiles, we suggest that the instability and magnetic reconnection make
a major contribution during the first and second fast acceleration phases,
respectively. Further, we find that both processes have a comparable
contribution to accelerate the filament in this event.
