A classic lie taught to children these days is that of the five senses. There are in fact far more than five senses, but the five described are simply the most obvious ones. All of them were evolved over the course of Earthling history at different times, and all of them play a huge part in allowing us to understand the world. Different animals rely on different senses to varying degrees, for example humans are often extremely dependent on sight, whereas the ability to smell is at this point more of a nice detail. For a dog however, their sense of smell alone can reach far farther than any human sense. Heck, they can even smell round corners! A dog is considered to be a rather intelligent animal. So is a human. But the two creatures certainly have a very different image of reality.
When we experience the world, we experience it through all of our senses simultaneously. However, despite being completely different processes, the information all converges into one clear picture in our mind. We see the sights, feel the feels, smell the smells, and bring it all together into our experiences. Think of the human mind as a T.V. set. It receives all these electrical inputs and radio signals and runs them through the magical refinery, spitting out an episode of Eastenders.
We look at a table and see a solid, still object. However, what we see is not at all the 'truth' of things. The table appears to be smooth on top, however we know that it is actually made up of atoms, molecules and particles. We cannot make out these individual building blocks on a table any more than an astronaut can make out individual trees on Earth. But, they are there. The problem is, human senses are focused on a larger scale than that. It wouldn't have done us any good to be able to know an atom when we see one across our evolutionary history, so we cannot view them with our naked senses. It is also worth noting that we do not 'see' the table. Our eyes merely trap a certain amount of light, which is translated into nerve impulses, which is then re-translated into what we 'see'. We think that when we wave our hands, we are controlling it because our touch information and sight information correspond, but that is merely because it is all we know. So already we realize we are severely limited in our senses: we can't see things that are too small, or too big. They may as well not even exist to us. We see colours only because of the available spectrum of light. There is no 'durple' light, so we are unable to see the colour 'durple'. In fact colour is an invention of the mind, just like sound.
If a tree falls in a forest with no-one to hear it, does it still make a sound? Well, yes. And no. If there is no-one to hear it of course there is no sound. There is merely vibrations of the air, that if a creature with an ear were to be in range of, could be converted into a sound in the mind. But what this problem really illustrates is not some pseudo-philosophical point, but rather that we are also severely limited in our perceptions of reality by language.
The popular Sapir-Whorff hypothesis illustrates this handily. It is, broadly speaking, the idea that what you call something matters. In the english language, we define sound in this context as 'vibrations that travel through the air or another medium and can be heard when they reach a person's or animal's ear.' This quite handily crushes the 'tree falling in the deserted forest' though experiment, as it becomes clear by the meaning of the words that there was no 'sound'. However, if sound merely meant: 'vibrations that travel through the air or another medium' then the answer would be different. This proves that 'truth' is a purely subjective concept, as different people will use different words to describe things. For example, a prosecutor might say 'This vicious beast savaged my client mercilessly leaving him deformed for life', and the defendant might say 'My harmless little pug only nibbled his finger a bit and gave him a couple of tiny scratches.
And the interesting thing is that this should all be self-evident, but humans are very concerned with the ego, and it is very good far the human ego to think that we are the pinnacle of evolution, gods among beasts, the only truly intelligent life on Earth. Many people would be entirely disconcerted to know that nothing in life could ever be held to be 'certain' or 'true', as there are many people out there who fear nothing more than the unknown, a fact we have only proved after centuries of fearing change, progress, and the unfamiliar.
