Reason is a faculty that prepares the soul for understanding. Capacity must be distinguished from realized knowledge, and sound inference from conjecture. Senses provide evidence about perceptible things; reason can connect established premises to conclusions beyond direct observation.
Self-evident knowledge requires no constructed argument once its concepts are clear. Inferential knowledge is obtained through reasoning. Necessary and acquired may also distinguish the role of personal choice and effort, depending on the technical usage.
Disagreement does not refute all valid reasoning, but every particular argument still needs examination. These distinctions frame the further question of whether inspiration (ilhām) qualifies as an independent source of knowledge.