Systems of knowledge is the systems by which people acquire knowledge. Knowledge is acquired through emotions. For example when you look at a painting, you will have a different emotion from another person. It is also acquired through myth and superstition. Through philosophy, which is concerned with physical things, one can also acquire knowledge. Philosophy is based on deduction and logical conclusion. Knowledge is also acquired in a scientific way. Science rests on absolute proof.
The first of natural philosophers is Thales who lived in the year 600 B.C. These were counted as the very first scientists. The most important characteristic was that he looked for himself. He is famous for the discovery of the water cycle. He deduced by logic that everything must be made of the same thing. This must be water. He thought of it as the basic element. Today in chemistry, it is proven that everything is made of the same thing but it is not water. He used methods used mostly in philosophy. The very earliest scientists or philosophers were termed as natural philosophers because they did not put their philosophy in practice. In those days, doctors and all those who worked by using their hands, were considered to be inferior to others.
Science was called philosophy. Sir Isaac Newton wrote one of the most famous science book "The Mathematical science of natural philosophy" which means physics. After 6th century B.C., science took a step backwards. In 4th century B.C. scientific ways were losing touch with reality. Plato came up with the idea that in our mind we have perfect forms of things we see around us. When we see a thing we match it with the perfect form in our mind.
Aristotle: came up with the idea that earth is round and is the center of the universe. People accepted this without any doubt until the early 17th century.
Galileo Galilei: wanted to prove that the sun was the center of the universe not the earth.
