Often, too, this becomes confused, and the two kinds of evidence appear contradictory to someone who harbours sophistry and heresy because of specious doubts that have taken hold of him. The defect lies in his perception, not in what he perceives—like a cross-eyed person who sees one thing as two, or a sick person who finds sweetness bitter. Otherwise, sound revelation is the truthful speech of one protected from error, whose reports cannot contain falsehood, whether deliberate or inadvertent.

Sound reason concerns what is established or negated in reality, not merely in the perception of a particular individual. Whatever is established or negated in reality cannot be reported otherwise by one who speaks the truth. Rather, whoever observes things as they truly are finds them consistent with the report of the truthful one.

As Allah Most High says:

“We will show them Our signs on the horizons and within themselves until it becomes clear to them that it is the truth. Is it not sufficient that your Lord is a Witness over all things?”
[Fussilat: 53].

He thus states that He will show them visible signs which they themselves witness, making clear to them that the Quran is true.

Allah Most High also says:

“And those who have been given knowledge see that what has been revealed to you from your Lord is the truth and guides to the path of the Almighty, the Praiseworthy.”
[Sabaʾ: 6].

Whoever has been given knowledge sees that what has been revealed to him from his Lord is the truth. But whoever possesses what he supposes to be knowledge—when it is actually ignorance—sees things otherwise than they truly are. Such is the person who deviated, so Allah caused his heart to deviate; whose heart contained a disease, so Allah increased his disease; who is among those whose hearts and eyes Allah turns away because they did not believe in it the first time; and who is among the deaf and mute