Faith and Reason
Iman and Kufr
Iman is conventionally translated as 'belief', and kufr as 'disbelief'. By extension, it is common to find some Muslims on this basis referring to the Qur'an to justify their categorisation of people into two simple camps, 'believers' who follow Islam, and 'disbelievers' who do not follow Islam. This, however, is fundamentally inaccurate.
The inaccuracy appears to derive from the precedent established by translations of Biblical texts into English, which mostly refer to faith and belief as largely inspirational matters unrelated to rationality or logic.
In fact, iman in Arabic does not denote blind belief. Rather, it literally means "attesting to the truth (of something) based on certainty (yaqeen) in it."
Notably, the Qur'an specifies a distinction between simply being Muslim, and being a 'mu'min' (often mistranslated as 'believer', but which actually means 'one who attests to the truth with certainty'):
"The Bedouins say, 'We believe.' Say: 'You do not believe; rather say, 'We surrender'; for belief has not yet entered your hearts. If you obey God and His Messenger, He will not diminish you anything of your works. God is All-forgiving, All-compassionate.'" (49:14)
Here, the term 'belief' can be more correctly translated in the text of the verse as follows:
"The Bedouins say, 'We attest to the truth with certainty.' Say, 'You do not attest with certainty, rather say, 'We surrender'; for certain attestation has not yet entered your hearts."
Here, we can see that 'one who surrenders' - a Muslim who ostensibly accepts the truth of Islam - has not necessarily become a true 'mu'min' achieving real inner certitude as to the truth. There is, rather, a distinction in this sense between a mu'min (mistranslated as 'believer') and a Muslim. In effect, the initial stage of deciding to become a Muslim is only the first step in the deeper journey of surrendering oneself to the Divine Reality, which involves attaining greater depths of inner certitude.
By the same token, the term kufr has been widely mistranslated as simply 'disbeliever', leading to much abuse of the word. As the antonym of the term iman, kufr literally means "refusal to acknowledge the truth (of something)", or "rejection/covering of the truth." As such, a "kafir" - one who practices "kufr" - is not a "disbeliever", but rather is someone who actively engages in the act of rejecting or covering the truth that comes to them.
In his seminal translation and commentary on the Qur'an, The Message of the Qur'an, Muhammad Asad explains this point in some detail:
"This meaning is easily grasped when we bear in mind that the root verb of the participial noun kafir (and of the infinitive noun kufr) is kafara, 'he (or 'it') covered (a thing)': thus, in Quran 57:20 the tiller of the soil is called (without any pejorative implication) kafir, 'one who covers', i.e., the sown seed with earth, just as the night is spoken of as having 'covered' (kafara) the earth with darkness. In their abstract sense, both the verb and the nouns derived from it have a connotation of 'concealing' something that exists or 'denying' something that is true. Hence, in the usage of the Quran - with the exception of the one instance (Quran 57:20) where this participial noun signifies a 'tiller of the soil' - a kafir is one who denies (or 'refuses to acknowledge') the 'truth' in the widest, spiritual sense of this latter term: that is, irrespective of whether it relates to a cognition of the supreme truth - namely, the existence of God - or to a doctrine or ordinance enunciated in the divine writ, or to a self-evident moral proposition, or to an acknowledgment of, and therefore gratitude for, favors received."
Thus, we find that frequently the Qur'an uses the word kafir and kufr in a way that is synonymous with ungratefulness to God, as opposed to any generic notion of 'unbelief' in a particular doctrine:
"And [remember the time] when your Sustainer made [this promise] known: 'If you are grateful [to Me], I shall most certainly give you more and more; but if you are ungrateful, verily, My chastisement will be severe indeed!' (Quran 14:7)
Here, the phrase "but if you are ungrateful" reads in Arabic "wa lain kafartum" - the Qur'an is thus applying the term kufr to the act of ingratitude. Similarly, another verse says: "And so, when they embark on a ship [and encounter danger], they call unto God, [sincere in their faith in Him alone]; but as soon as He has brought them safe ashore, they [begin to] ascribe to imaginary powers a share in His divinity: and thus they show utter ingratitude for all that We have vouchsafed them, and go on [thoughtlessly] enjoying their worldly life." (Quran 29:65-66)
Here again, the erosion in sincere acceptance of a previously accepted truth due to forgetfulness of God's powers and thus reliance on powers other than Him, is equated with ingratitude, and further is applied to people who ostensibly do 'believe' in God.
In a similar vein, the Qur'an relates a conversation between two people, one of whom is a 'believer' in God's existence and who has been blessed with God's bounties - who then tells his friend that even if he meets Allah, he expects to enter paradise. In response, his friend accuses him of kufr:
"His companion rebuked him during the conversation, saying, 'Do you disbelieve in the Being Who has created you from clay (i.e. your father Adam), then from out of Nutfah (mixed semen drops of male and female discharge) and then shaped you as a man?" (Quran 18:37)
In his commentary on this verse, Sayyid Abul Ala al-Mawdudi, in his Tafhim al-Qur'an, concludes that:
"This shows that 'unbelief' [kufr] in Allah is not confined to the denial of the existence of God in so many words, but arrogance, pride, vanity... Although that person did not deny the existence of Allah, his companion charged him with unbelief [kufr] in Allah. This is because the person, who considers his wealth and his grandeur etc., to be the fruits of his own power and capability and not the favours of Allah, and who thinks that they are everlasting and none can take them away from him and that he is not accountable to anyone, is guilty of 'unbelief in AIIah' [kufr], even though he might profess belief in Him..."
Here, it is clear that the mere act of holding an incorrect belief in the nature of God was not sufficient to label that individual as someone 'outside' the fold of Islam, and not a Muslim. Despite that, his culpability in kufr due essentially to his arrogance and egoism is unequivocally acknowledged. Kufr, then, is not an act or condition that can be easily discerned by someone's professed beliefs. By extension, a seemingly believing and outwardly religious Muslim can commit kufr - yet the Qur'an does not identify any outward penalties or consequences at all for this.
Ultimately, the Qur'anic concepts of iman and kufr can only be properly understood in the context of the following verse:
“Allah only charges a soul according to what has come to it” (Qur’an 65:7)
A person is only responsible for attesting to reality of which they become aware - they cannot be held responsible for denying, or rather covering/rejecting something whose truth they are not even aware of. This clarifies that iman and kufr are therefore inward states that ultimately denote the cognitive response of a person to the communication of something which is true.
This is why the Qur'an categorically confirms that the label of kufr is not a label that can simply be thrown around and applied to anyone one chooses. Even Prophets have refrained from doing so. For instance, when Musa leads his believing followers across the sea, they leaned toward idolatry, but this did not cause Musa to reject them as 'kafirs':
"We delivered the Children of Israel across the sea. When they passed by people who were worshipping statues, they said, 'O Moses, make a god for us, like the gods they have.' He said, 'Indeed, you are a people who know not." (7:138)
Here, Musa calls them "ignorant", not 'kafir', despite their clear aspiration to worship entities other than the ultimate Godhead.
It is therefore clear that within the Qur'an, there is no simplistic distinction between Muslims and non-Muslims which equates to 'believers' and 'disbelievers.' Rather, a proper reading of the specificities of the Qur'anic text show that Muslims and non-Muslims alike are capable of engaging in acts of iman and kufr depending on their degree of exposure to truths.
Muslims are challenged as to whether they truly hold iman although their affiliation to Islam is taken for granted. Kafir is a designation not for a "non-Muslim", but rather far more specifically for an individual who rejects and actively seeks to suppress the truth that comes to them, a condition that can easily apply to a Muslim.
By the same token, the Qur'an frequently recognises that non-Muslims - people who do not accept the truth of Islam - may still retain 'iman', and be 'believers' who "do good deeds." Such non-Muslim groupings are referred to explicitly and repeatedly in the Qur'an in different ways, most commonly as 'People of the Book' (with reference to those affiliated to the Abrahamic faiths of Christianity and Judaism), but also extending beyond that.
Prohibition of Takfir
It is precisely for this reason that the Prophet repeatedly said that the simple declaration of acceptance that "There is no god but God," is sufficient to consider someone a Muslim, and that labelling such a person a kafir is prohibited:
"Withhold your tongue from those who say 'There is no god but God' - do not call them kafir. Whoever calls a reciter of 'There is no god but God' as a kafir is nearer to being a kafir himself." (Tabarani, reported from Ibn Umar)
The Prophet also spoke not just condemning the labelling of Muslims as kafirs, but also labelling of 'believers' generally, where as noted above, 'believers' can be Muslims or non-Muslims, including people who do not follow any particular religious scripture:
"Whoever attributes kufr to a believer, he is like his murderer." (Sahih Bukhari, Book of Ethics, Book 78, chapter 44)
The problem here of course is that a person's nature and sincerity of 'belief' cannot be known by anyone except God The broad prohibition on labelling anyone a kafir is stipulated clearly in the Qur'an:
"Oh you who believe! When you travel in the cause of God, investigate carefully, and do not say to anyone who offers you peace, 'You are not a believer!' coveting the perishable goods of this world. With God is plenteous bounty. You too were such [not a believer] before, until God granted favour on you. Therefore take care to investigate, for God is aware of what you do." (4:94)
As Dr. Louay Fatoohi explains, this verse was directed at ensuring that Muslims would not attack non-Muslims they encountered on their travels on the pretext that they are 'disbelievers,' if they offered peaceful relations.