Do the two noble verses (and among you is he who is returned to the most abject old age so that he knows nothing after having known) mean that a person forgets all of his knowledge or some of it, and do they refer to the same meaning? And what are the sayings of the people of knowledge regarding their interpretation? And is the word "nothing" for the whole or a part?

Allah created people to progress from weakness to strength, and then from strength to weakness. Some are reduced to the feeblest of old age, a stage where a person's outward and inward faculties, including the mind, become weak. And His saying, the Almighty: "so that he may not know anything after having known much" (Quran 22:5), means the predominance of ignorance, not the complete absence of knowledge, because some who advance in age may retain their intellect, hearing, and sight.