In order to clarify the subject of the discussion, it is necessary to mention the following points:
1. Being an intellectual school, Shia accepts rational principles and standards which are also endorsed and approved by Shari’ah. The precedence of these principles over every other belief is a part and parcel of Shia belief and which Shia is also proud of. For instance, when it is proved in theology that God cannot be physical in the sense of being composed of, or containing, matter or energy, then we cannot interpret the verses that indicate physicality of God in a literal way. In fact, we must see what those verses actually mean and that meaning certainly does not imply physicality of God.
2. The verses of the Quran have the capability and capacity to interpret one another. At times, we must not interpret even one verse without taking other verses into consideration. In fact, we may have to take several verses and the context into consideration in order to find the right meaning of a verse. If we interpret one verse without considering the preceding and succeeding verses into account, we will not be able to understand the reality of the Quran.
Having said that, we will now turn to the main discussion, i.e. infallibility. Infallibility or inerrancy of the Prophet is one of the beliefs for which different rational arguments have been put forth and lengthy discussions have taken place around it in theology.
In addition to rational arguments, there are also some Quranic verses which indicate that the Prophet is infallible and that he does not err: "He (alone) knows the Unseen, nor does He make any one acquainted with His Mysteries,- Except a messenger whom He has chosen: and then He makes a band of watchers march before him and behind him - That He may know that they have (truly) brought and delivered the Messages of their Lord: and He surrounds (all the mysteries) that are with them, and takes account of every single thing." The verses which refer to this belief are too many and they have been mentioned in different books.
As opposed to these rational and textual proofs, there are some verses and narrations which ascribe error to the infallibles ranging from Adam (a.s.) to the Prophet of Islam – peace be upon him and his family. Among the verses which call on the Prophet to seek divine forgiveness is the following verse: “So know that there is no god but Allah, and, ask protection for your fault and for the believing men and the believing women; and Allah knows the place of your returning and the place of your abiding. “
Such verses, if compared with the verses regarding infallibility, are less strong because the verses concerning infallibility are explicit and inconspicuous.
Generally speaking, these verses and applications of such nature can be summed up in the following meanings:
1. The word “sin” in these verses refers to abandoning a preferred action which is not opposed to infallibility but at the same time it creates a need for repentance and seeking divine forgiveness. Most of these verses refer to abandoning a preferred action which is why the Prophet (pbuh) was commanded to seek divine forgiveness.
2. At times, repentance or istighfar (seeking divine forgiveness) goes out of what is considered to be a normal repentance. It is just an excuse for a talk between the lover and the beloved. For example, the Commander of Faithful, Imam Ali (a.s.) says: «کَیْفَ أَسْکُنُ فِی النَّارِ وَ رَجَائِی عَفْوُک» (Or, how may I reside in the fire [of hell] while my hope is Your forgiveness?) In order to understand the truth and the cause of this saying, we can say a lot of things but apart from that we must consider it probable that such statements should be treated as “love talk” between lover and the Beloved. They should not be confined to their apparent and literal meanings.
 Vide Indexes: “Infallibility of Prophets from the Perspective of the Quran”, question 15798; “The Necessity of Infallibility and Ways to Distinguish It in the Imam (a.s.)” question 5548; “Infallibility of Moses and Killing the Coptic”, question 3452; “Infallibility of Prophet (pbuh) and Leaving What is More Preferable”, question 20724.
 Jinn, 26 – 28; Vide: Tabatabai, Sayyid Muhammad Hussein, Al-Mizan fi Tafsir al-Quran, vol.2, p. 134 – 139, Islamic Publications Office, Qom, fifth edition, 1417 A.H.
 Ta-Ha, 121: “Then they both ate of it, so their evil inclinations became manifest to them, and they both began to cover themselves with leaves of the garden, and Adam disobeyed his Lord, so his life became evil (to him).”
 Muhammad, 19.
 Makarem Shirazi, Naser, Tafsir Nomouneh, vol.21, p. 452, Dar al-Kutub al-Islamiyah, Tehran, first edition, 1374 A.H.
 Tusi, Muhammad bin Al-Hassan, Mesbah al-Mutahajjid wa Selah al-Muta’bbed, vol.2, p. 847, Fiqh al-Shi’ah Institute, Beirut, first edition, 1411 A.H.