How do we know what we know and what relation does what we know have to external reality?
We live in a world of objects. If we examine the visual sensory apparatus, we find that light strikes objects in the external world and the reflected light enters our eyes through the cornea and is focused on the retina. The retina consists of specialized nerve endings called rods and cones. When struck by light, the rods and cones fire, sending a nerve impulse along a strand of the optic nerve which ends up in the cerebral cortex. The optic nerve consists of millions of strands of nerve fibers and from the perspective of the brain, it receives a high volume of what would look to be a random series of nerve firings across a vast array of nerve fibers. It is the job of the cerebral cortex to sort this apparently random data out and make sense of it.
How does this happen? As far as I have been able to determine, it is through a rather elaborate hierarchy of patterns stored in the cerebral cortex. When a pattern matches the data, the process we call recognition occurs, the data makes sense. Everything that we recognize in the external world goes through this process. I won't go into how the brain "boots up", how it develops the patterns, but that process and the understanding of it is the essense of learning. Not only is everything we know in the world a product of this process, but even our very perception of space and time and our ability to navagate through 3 dimensional space and organize our thinking in a temporal context are a result of organizing data based on the matching of pre-existing patterns with the data, yielding recognition.
This may all seem to be rather straight forward, but we have to also take into account that this thing that we usually refer to as "myself" also appears in the world and also must itself be represented by a hierarchy of patterns built up over the course of a lifetime. In fact it can be demonstrated that without a pattern that creates a basic division of all patterns into 2 distinct divisions: self and other, the functioning of all other patterns will not yield functional recognition. Self awareness is an early and significant event in child development.
The thing that must be grasped here is that we "assume" that the world is an objective reality, ie. if the tree falls in the forest, and no one is there to hear it, the tree still falls non-the-less. The problem with this assumption is that it is just that, an assumption. The independent existence of the so called external world, apart from the mind which perceives it cannot be demonstrated. Why? Simply because any experiment designed to prove the independent existence of the external world is dependent on the mind and it's process of pattern matching. Because of this there can be no certain way to determine what in the recognized object has been contributed by the data and what has been contributed by the patterns.
What we do to get around this problem is to set up a system of agreement which allocates "reality" to what we can agree on. Does the Earth go around the Sun? Or does the Sun go around the Earth? To most people the answer is obvious, but it is the very obviousness of the answer that reveals the bias in our thinking. To the people who lived before Galileo, the answer was also obvious, so obvious in fact that they were willing to kill people for suggesting otherwise. But is our perception of the solar system and 3 dimensional space the end of understanding and growth in understanding? One day we will look back at the 20th/21st century understanding of how space is structured, with planets revolving around Suns and laugh at our failure to perceive the most obvious. Remember that the new understanding is always a simplification. Our models become more and more complex over time until a new one is created that eliminates the complexities through a new and more deep understanding. There is no end to this process. There is no place we can stand and say: "This is it, no more change is possible."
And the human mind is an integral part of the process because it is the reality, consensual and otherwise that arises out of the functioning of the physical brain. Mind and it's perception of reality is a non physical construct that exists in a totally separate domain from the physical world but the two mutually influence each other creating civilization as we know it. If we would change the world, we need to start at home, working on the model. We need some "bunker busters" to soften up our understanding of what is.