However, there is a need to correct errors, isn't there? For example, the Third International was an effort to correct the Second International, wasn't? Wasn't the support for WWI by the socialist deputies an egregious error? Wasn't it rooted in theory, as well as the compromised social situation of trade union leaders and parliamentiarians? By the same token, didn't the Third International spawn defeats on account of theoretical errors? Wasn't the "third period" partially responsible for Hitler's victory? Didn't the Popular Front strategy help Franco come to power? The Fourth International was an attempt to return Marxism to its original critical and revolutionary path, but failed for reasons I have gone into elsewhere. All this has nothing to do with the Doctrine of Progress, but the merciless dialectic of dialectical materialism criticizing itself and moving forward.
Louis Proyect (http://www.panix.com/~lnp3/marxism.html)