الْمُدْرَكُ ... وَالْآلَةُ ... وَالطَّرِيقُ
The object or proximate factor, the instrument, and the route.
“Cause” is not always used for the same kind of influence. The eye is an instrument of seeing, a report is a channel of information, and intellect is a faculty of understanding and inference. Describing all three without qualification as things that “produce knowledge” conceals their different roles.
A student hears a mathematical explanation: a teacher's words convey information, the ears register sounds, and reason grasps the proof. These aspects can cooperate in one acquisition of knowledge. Classifying means of knowledge requires specifying the respect in which each is called a cause.