The reader will see that Bukharin’s example was meant to give me a popular explanation of the harm of one-track thinking. I accept it with gratitude, and in the one-good turn-deserves-another spirit offer a popular explanation of the difference between dialectics and eclecticism.
A tumbler is assuredly both a glass cylinder and a drinking vessel. But there are more than these two properties, qualities or facets to it; there are an infinite number of them, an infinite number of “mediacies” and inter-relationships with the rest of the world. A tumbler is a heavy object which can be used as a missile; it can serve as a paper weight, a receptacle for a captive butterfly, or a valuable object with an artistic engraving or design, and this has nothing at all to do with whether or not it can be used for drinking, is made of glass, is cylindrical or not quite, and so on and so forth.
Moreover, if I needed a tumbler just now for drinking, it would not in the least matter how cylindrical it was, and whether it was actually made of glass; what would matter though would be whether it had any holes in the bottom, or anything that would cut my lips when I drank, etc. But if I did not need a tumbler for drinking but for a purpose that could be served by any glass cylinder, a tumbler with a cracked bottom or without one at all would do just as well, etc.
Formal logic, which is as far as schools go (and should go, with suitable abridgements for the lower forms), deals with formal definitions, draws on what is most common, or glaring, and stops there. When two or more different definitions are taken and combined at random (a glass cylinder and a drinking vessel), the result is an eclectic definition which is indicative of different facets of the object, and nothing more.
Dialectical logic demands that we should go further. Firstly, if we are to have a true knowledge of an object we must look at and examine all its facets, its connections and “mediacies”. That is something we cannot ever hope to achieve completely, but the rule of comprehensiveness is a safeguard against mistakes and rigidity. Secondly, dialectical logic requires that an object should be taken in development, in change, in “self-movement” (as Hegel sometimes puts it). This is not immediately obvious in respect of such an object as a tumbler, but it, too, is in flux, and this holds especially true for its purpose, use and connection with the surrounding world. Thirdly, a full “definition” of an object must include the whole of human experience, both as a criterion of truth and a practical indicator of its connection with human wants. Fourthly, dialectical logic holds that “truth is always concrete, never abstract”, as the late Plekhanov liked to say after Hegel.
(Let me add in parenthesis for the benefit of young Party members that you cannot hope to become a real, intelligent Communist without making a study—and I mean study—of all of Plekhanov’s philosophical writings, because nothing better has been written on Marxism anywhere in the world.)