Original sentence: According to Tabatabaei, Ismah indicates presence of a quality in man which protects him from committing sin or error.He identifies this quality with knowledge.However, contrary to ordinary people where knowledge is imperfect and the virtues can be occasionally overpowered and comprised by desires and vices, Prophets are bestowed by a supreme knowledge and spiritual faculty that always remains unaffected.Ismah, thus defined, doesn't nullify the Prophets' free will to choose whether or not to sin.Likewise all virtues such as bravery, chastity and generosity are forms of knowledge deeply rooted in human psyche enabling the person to abstain from indulging in their respective two opposite extremes, i.People differ in the extent of their obedience and disobedience to God according to their respective degrees of knowledge and will.This unique merit in Prophets is called Ismah.as cowardice vs.dissipation and miserliness vs.recklessness, austerity vs
Edited sentence: According to Tabatabaei, Ismah means a presence in a man which protects him from committing any sin or error.He further argues that people differ in their obedience and disobedience to God based on their respective degrees of knowledge and volition.Tabatabaei regards every deed or attribute as a kind of knowledge with its root in the psyche which creates its own effects on person's behavior, and knowledge does not prevent  from committing or not committing an action.The prophet's spiritual faculty which protects him from committing sins is based on his knowledge