Classes' as regards to knowledge -

There are 4 kinds of knowledge, based on the 2 kinds of distinctions - 'Commonly known' v/s 'Rare', and 'General' v/s 'Specific'.

Commonly known + General - All cars run on wheels.

Commonly known + Specific - Einstein's first name was Albert.

Rare + Specific - Rwanda's capital is so and so.

Now comes Rare + General. The trick here is as follows. If I say 'cricketers wear black bands on their arms while playing a match if someone from the fraternity has passed away recently', then you will say that yes, this is rarely known but not quite general, because it pertains (specifically) to cricket only. So it should be in the Specific + Rare category. And if you say - "wait, is it so that all sportspersons wear black bands in such cases?", to make it fit in the Rare + General category - it would occur to you - "oh, how come I didn't know such a prevalent/common general fact (prevalent across all sports)?" So it should then be in the General + Common category. In either case, there doesn't remain anything in the 'Rare + General' category. This is a property of commonsense knowledge - there is nothing easily fittable in the 'Rare + General' category of knowledge.