The point is (as it seems this is what none is getting at), the way in which we interact with the world is through language and how our brain uses our language to interpret it. Language itself is abstract and the words we use to describe an object as in themselves abstract. A circle does not physically exist, nor does an edge, because these are terms we use to describe something specific, but only something that's specific to how our minds interpret it. So lets take 'circle' again, it is only something we give to an object as a property. Take a donut, we'd say that it's circular. Would a culture whose language has no concept of a circle or even shapes for that matter understand that the a donut is circular? The donut doesn't cease to exist, it's just a 'circle' is just a concept we apply, therefore it's abstract.
Equally if a culture had no concept of a 'edge', you would not be able to tell them the edge of a knife is sharp until you bring them the concept of an 'edge' to their language.
Arguably, even the term 'knife' is just an abstract, because a knife is just how we define a piece of metal with a particular form and metal is an abstract because it's just molecules of a certain form and well, you get the idea.
I think here's an interesting experiment as far as 'language' and 'reality' goes, it's the Loftus & Palmer one on Eye Witness testimony. Essentially they had people watch a video of a car crash and at the end they took to different groups of people to ask the same set of questions but worded differently. They would be asked, "at what speed do you think the car was going when it [insert word] with the other car" the replacement word could be 'crash', 'collided', 'hit', 'smash' and so on and they would have a follow up question, which would be, "was there broken glass afterwards?" The highest speeds given went to 'smash' and generally people said that there was broken glass at the scene, whilst others with 'lighter' words tended not to suggest so. This experiment has been repeated of course and it kind of caused a little bit of a stir with how we understand the reliability of eye witness testimony. Through simple word play how people remembered something they've only just watched was altered. More info here.
I think what it comes down to is that we're connected to the world through language and how we use language to interpret any sensory data our brain receives. Essentially, our own realities exist in our cerebral cortex.
Also start considering how people's interpretations of events are affected by their perception of reality, what about a near death experience, I am sure a psychologist and a priest may interpret their experiences very differently and use completely different words to describe it and essentially tell a different story of what could be the same experience.
Of course, I've gone off track from whether an 'edge' exists, but it kinda hits on how we 'view' the world relies on language and is full of concepts that do not physically exist, but are used to apply properties to things that do.