One possible categorization of knowledge is the common way that introduces Science as a distinct knowledge body. It is worth noting that this common categorization is no way the only possible categorization but for reasons unknown to me it has proven itself the most efficient one ever used in terms of longevity, prosperity and environment control for human beings.

Knowledge can also be viewed in a hierarchical tree of different abstraction levels; each level possibly introducing totally new concepts as a result of synergy, the fact that each level is not necessarily a superposition or union of the subsets of its preceding level. In this hierarchical manner of classification sensory information are perhaps of the lowest abstraction degree while their symbolic notation, the language, makes the next level of abstraction and so on.

I suppose all measures taken to study knowledge in content and form (structure) are in vain or at least fruitless. All these studies are themselves knowledge packets that will become parts of the same knowledge they're devoted to study. Thus, they don't qualify for assessing the content or the form. Because of this supposition, I assume that verifiability, portability (eg sharing), nature, definition and limits of knowledge are subject to uncertainty, even the uncertainty itself.

The above description of my opinion of knowledge is also subject to such uncertainty and that's why there is a logical loop in the very first definition of knowledge. This logical loop and many similar loops have their roots in that that we have always taken for granted what we could never have been sure of.

More important, when knowledge - being the most important aspect of all discussions - is subject to such controversy, no other aspect is safe from these controversies. Therefore, no discussion can be carried out without encountering the same problem over and over but in different semblances.