= Solution
\b[<Slab pull> is generally the largest direct driving contribution for plates attached to substantial cold descending <slabs>.] Cooling makes <oceanic lithosphere> negatively buoyant; sinking <slabs> transmit a pulling force to the rest of the <tectonic plate>. The comparison is a force balance, so the following driving and resisting processes both matter.
* <Ridge push> is gravitational sliding away from an elevated <spreading ridge>. Cooling, contraction and deepening of <oceanic lithosphere> establish the lateral difference in integrated <pressure>; <ridge push> is not simply <magma> squirting sideways into a plate.
* <Basal traction on a tectonic plate> transfers <shear stress> between the <lithosphere> and circulating <mantle>. It can help or oppose <plate motion>, depending on their relative <velocities>. <Slab suction> is the contribution of <slab>-induced <mantle flow> and its associated <pressure> and <traction> to nearby <plate motion>.
* <Frictional sliding> along <faults>, shearing along the plate interface, bending of the incoming <slab> and <viscous dissipation> in the surrounding <mantle> resist <plate motion>. <Continental collision> introduces additional resistance through buoyancy and deformation of thick <continental crust>.
* <Mantle plumes> and <continental rifting> can locally promote uplift, weakening and separation, but do not provide a universal explanation for all <plate motion>.
The first two gravitational contributions ultimately belong to the same coupled <mantle convection> system: the plates are its cold upper <thermal boundary layer>. They are not passive rafts on a prescribed conveyor belt. A plate with little attached descending <slab> need not have <slab pull> as its largest local driver, and a large gross <slab pull> can be partly consumed by bending and interface resistance. Geological observations and force comparisons nonetheless support the general dominance of <slab pull> for rapidly moving subducting plates.<What causes earthquakes? by British Geological Survey>[Section explaining mantle circulation, ridge push and slab pull, including the association between subducting plate edges and faster motion.]{ref}
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