End Post: What is Constructed, What is Not?

I think that some things exist which are almost certainly wholly or partially constructed, some which are almost certainly not, and some the status of which one cannot currently determine with any certainty.

In the first category lie ideological concepts and concepts people impose on reality to explain it - patriotism, nations, race, systems of temporal and spatial measurement, mathematics, etc.  These may be grounded in reality, but they themselves are totally apart from it; the idea of nations may stem from humans' primitive urges to mark out territory, but the idea itself does not exist anywhere except in constructed ideological space - a 'nation' is not a physical thing, or an urge, even if it exists because of one.

In the second is a large part of the external world.  While of course fallibility, as always, is an undeniable possibility, discarding that I believe one can be relatively certain that the world exists.  One does not really have any reason to doubt its existence.  Most people think, at least, that they can tell the difference between dreams and reality, and while they possess no method of proving that they are not asleep, they have no particular reason to think they are.  Furthermore, other people seem to exist as well.  One cannot accurately predict their actions, read their thoughts, or cause them to comply with one's wishes if they do not want to.  Certainly, the wills and minds of others could actually be hidden parts of one's own psyche, subconscious parts, but this seems far-fetched, and once more, there is no especial reason to believe it is so - while there is reason to believe it is not (one's experience of the world).

The last category contains the actual thing that is (or is not, if it does not exist) time, some deities, and some sensory perceptions.  As I still have no idea what time actually is, I do not know if it exists or not, is constructed or not.  Certain deities (and imaginary objects or concepts) have unknowability included in their definitions - this sets them apart from material objects, or imaginary objects.  While I can say with a certain level of confidence that the material chair upon which I am sitting exists (since the definition of a material chairs says that if I am sitting on it I should be able to feel it, see it, etc.) and that there is no material chair on my head (because, by the same definition, I should be able to experience it with my senses if it does), I cannot say whether a transcendent, immaterial chair, undetectable by any means known to humanity, is on my head.  I have no particular reason to believe that it is - I also have no particular reason to believe that it is not.  Yes, I have never encountered such a chair before to my knowledge, nor anything like it, but of course I would not have known if I did because it would have been undetectable!

I cannot think of anything which does not  fit into one of the above three categories.  If anyone else can, please feel free (more than free - invited!) to comment.