....Subduction
           (...the Far Side of Ridge Spreading) 

This has probably been said before but it bears a stand-alone page repeat - if subduction were to occur, then the continents would never separate and there would be no Plate Tectonics. Why?  Because as soon as the continents tried to separate (because of a spreading ridge developing between them - as in the Atlantic, say) that growth of ocean floor would be matched by destruction at the other,  ..the opposite, .(the 'far') side.

Some otherwise sensible people find this hard to grasp, but it's quite simple.  However you have to start from the two premises of Plate Tectonics.  First, subduction is the driver for Plate Tectonics, i.e.,  the opening of the continents is driven by subduction.  Opening is not driven from the ridges.  Ocean floor spreading can only happen to the extent that subduction occurs, otherwise opening would be being driven from the ridges, which the new, goalpost-shifted version of Plate Tectonics says doesn't happen. Second, the cycling of subduction and ridge spreading is independent of the width of continental separation, i.e., subduction can happen just as easily in a narrow ocean as in a wide ocean.

So if there's no subduction then there can be no cycling convection and no opening of the continents.  But (says Plate Tectonics) subduction does happen.  But that means that the continental buttress up against which the ocean floor is subducting must be fixed, ..not moving, ...otherwise there would be driving from the ridges - which Plate Tectonics says there isn't.  (There used to be, mind you, ..called "ridge-push" but with ridge-push pushing at one end and subduction pulling at the other end that ran up against the problem of convection as a runaway perpetual motion machine.  Ridge-push is now palmed off as a gravitational collapse, cooling/ shrinking phenomenon - albeit still dependent on subduction).

And if the continental buttress against which subduction is happening is fixed, and there is no opening driver at the spreading ridges, then at any particular point in time the continental lithosphere is not opening; in effect the action of subduction is linked to the fixity of continental separation no matter how widely spaced this is.

So (the first principle above), if there is no subduction, then there is no cycling of 'convection', no opening of the oceans, and no Plate Tectonics.

And (the second principle above), if there is subduction, then the continents would never open, because continental separation is fixed at the point when subduction begins, i.e., there is destruction of the ocean floors as soon as they try to initiate. So the continents would never separate and an ocean floor would never open.

So just on grounds of conceptual implications alone, and whichever way you look at it, subduction precludes Plate Tectonics.