Whether the source of all knowledge is internal or external is what we wish to address in this write-up. We define knowledge as it is defined colloquially. By external we mean whether knowledge comes from things external to us, like books, teachers, fellow-students, etc. and by internal we mean whether knowledge comes from within us, i.e., as a reaction to the things external to us.
Let's take an example of Newton's laws of motion. Does one need an external source of knowledge to arrive at the laws of motion? The answer is no, reproducibility is a property of Science, so one could just observe how things move and arrive at them. One doesn't need any external source of knowledge, like books or professors, in order to learn Newton's laws of motion. It's just because we wish to save time that we have external sources like books, i.e. we wish to not re-invent the wheel, so to speak, and focus on learning "unknown" laws of Nature instead of "known" ones.
Similar to the laws of motion, one doesn't need any external source to learn any of Nature's laws. One could learn them by observing, questioning, and reflecting. So, the source of knowledge is internal, not external. This post is related to the previous post, "A perfect language".