Adler portrays knowledge as knowing the “truth”. The two kinds of truth are theoretical and practical truth. Theoretical truth taken from what you see, experience, and can describe while practical truth taken from ethics or doing what is right. There are many kinds of knowledge such as common-sense knowledge, knowledge obtained from scientific and historical research, and finally the knowledge of reality, like nature of being. He makes sure that we understand the difference between knowing something and understanding something. He believes that knowledge and understanding are the exercises of an intellectual virtue that provides a guideline for making important decisions.
Immanuel Kant’s Copernican revolution transformed philosophy. Kant was able to finally link rationalism to empiricism and no one could debate of reality or knowledge without understanding the human mind in the development of reality and knowledge. Philosophers such as Aristotle, Aquinas, and other philosophers from that era were all realists who believed that science aims at truth and that people should consider scientific theories as being indisputable, or likely accurate.
Mortimer Adler had a different approach to the thought of science. He is right when he says, “no science that is applicable to the understanding of the sciences themselves”. I don’t think of philosophy and history as being a science