Technological grounds

For the occurrence of communism on the basis of each member getting what they need while each member puts in what they want , one needs the technology to empower productivity to the point where one person could single-handedly take care of the needs of a cell in such a society for its needs. There is necessity for a willingness by every member to cover that duty at least without sacrificing more than 20 hours per week.
Such an ultraproductive state would achieve much more however...
Since these two limits are set we can make a guess when communism can arrive if we assume continuing social and  economic progress.

To know what we state or ...

It certainly seems reasonable to know everything we can know about the statements we utter. Is it, however reasonable to say what is without knowing it all.
It is possible we have not yet attained knowing of a certain fact, but in the process of argument or even a monologue one comes to it. Such knowledge by insight does happen occasionally. Just recently I attempted to convince my friend of his error when I suddenly understood my own mistake. The endeavour concluded with an insight of just such a nature!