Have you ever heard of Nietzsche?
One of his greatest theories was that truth doesn't exist. In fact it exists, but we, humans, can't desbribe (verbally) anything and ensure/prove that that is true.
The chair example: What is a chair? A material where you sit? So a "table", the "floor" and a "bed" are also chairs. You can sit on them. And then you make a complete description of a chair, but there are many types and styles of chair, with different materials, shapes, etc.. So if I create a chair-table, how can you say that's a chair and not a table, or vice-versa? The point is, chemically, physically, geometrically and philosophically speaking, there is nothing to comprove that something is a chair, or any other object.
There are very, very, VERY few things that can be proved to be what they are; so, in Nietzsche's theory, most of the true (like 99.999999999% of the true) is relative.
But what I just said was the philosophical theory; when it comes to common sense things are completely different.