smell, the sense of taste, and the sense of touch. Through reason together with hearing, one perceives speech and all audible sounds; through reason together with sight, one perceives all visible bodies, accidents, and individual entities; through reason together with smell, one perceives all odors; through reason together with taste, one perceives all flavors; and through reason together with touch, one perceives all tangible things, with their differences in softness, roughness, and the like.
The third is mass-transmitted reports. Through these, one learns of distant lands, past generations, the advent of the Prophet, his call to Islam, and similar matters.
Section
Knowledge attained through these three means is necessary knowledge: it impresses itself upon the mind so inescapably that the mind can neither free itself from it nor doubt it.
The fourth means by which knowledge is attained is reflection and inference. Reflection and inference rest upon necessary knowledge, upon what rests upon necessary knowledge, or upon what rests upon something that itself rests upon necessary knowledge—and so on, as far as it can be accurately grasped and its existence established.
For example, a person necessarily knows that he exists. This is a foundation upon which necessary kinds of knowledge are built. Once I necessarily know that I exist, I consider whether I have come into being or am eternal. I cannot properly undertake this inquiry before knowing that I exist. When I reflect correctly, I come to know that I have come into being. Thus, knowledge that I have come into being is inferential knowledge, founded upon the necessary knowledge of my own existence.
Then, once I know that I have come into being, I consider whether there is one who brought me into being or not. Through correct reflection, I come to know that there must be one who brought me into being. This, too, is inferential knowledge founded upon inferential knowledge, which in turn is founded upon necessary knowledge. Then I also reflect further on the one who brought me into being: whether