Sharp philosophical discussions renter on human knowledge, and these discussions occupy a central position in philosophy, especially in modern philosophy. Knowledge is the starring point of philosophical advance toward establishing a solid philosophy of the universe and this world. As long as the sources of human thought, its criteria and its values, are undetermined, it will not be possible to carry on any study, regardless of its kind.
One of the above-mentioned wide discussions is that which handles the sources and primary origins of knowledge through investigations, studies and attempts to discover the primary principles of the powerful intellectual structure with which the human race is endowed. Thus, it responds to the following questions: ‘How did human beings come to know? How was their intellectual life formed, including all the thoughts and notions it possesses? And what is the source that provides them with this stream of thought and knowledge?’
Every human being knows numerous things in his life, and numerous forms of thought and knowledge are expressed in his soul. There is no doubt that many kinds of human knowledge grow out of each other. Thus, in forming new knowledge, a human being is assisted by previous knowledge. The issue is to be able to put our finger on the primary threads of thought and on the common source of knowledge in general.
To begin with, we must know that in the main, perception is divided into two kinds. One of them is conception.  This is simple knowledge.  The ether is assent. (p. 58) This is knowledge involving a judgement.  Conception is exemplified in our grasp  of the idea of heat, light or sound. Assent, on the other hand, is exemplified in our judgement  that heat is a power derived from the sun, that the sun is more luminous than the moon, and that the atom is susceptible to explosion. 
We begin now with a study of human conceptions, concentrating on their sources and causes. After that, we will take up assent and knowledge.