without faith: not believing, whether of a person who fails to trust or, as a noun, of someone who stands outside the faith
TranslatabilityApproximateCertaintySettled
This is the plain opposite of "believing." Greek builds it by putting a negative prefix on πιστός, the word for faithful or trusting, so at its core it names a person marked by the absence of faith.
The New Testament uses it two ways that shade into each other. Sometimes it describes people who ought to trust but do not, a lapse in faith rather than a settled identity: Jesus calls the crowd around him a faithless generation, and the risen Jesus tells Thomas to stop being unbelieving. More often, and especially in Paul, it works as a noun for a whole class of people, the unbelievers, meaning those outside the community of faith. In that use it marks a boundary: believers are warned not to be mismatched with unbelievers, spouses may be believing or unbelieving, and lawsuits should not be dragged before unbelievers.
The two uses are not two different words. Both rest on the same idea of a life without trust in God. The difference is only whether the writer is pointing at a momentary failure to believe or at the standing group of people who have not believed at all.
Nuances
1aan unbeliever: a person outside the community of faith, one who has not believed
1bfaithless: failing to trust, said of someone who ought to believe but does not
Mat 17:17Mrk 9:19Luk 9:41Jhn 20:27
2
incredible: not to be believed, too much for the hearer to accept
TranslatabilityApproximateCertaintySettled
The same word can turn the other direction and describe not the person who fails to believe but the thing that seems impossible to believe. Instead of "one who does not trust," it means "something that cannot be trusted as true."
The New Testament uses it this way only once, when Paul asks his hearers why they judge it beyond belief that God raises the dead. The point is that the resurrection strikes them as incredible, a claim they cannot bring themselves to accept, not that anyone lacks faith. This flip between the person who disbelieves and the thing that is disbelieved is common for words of this shape in Greek, and the surrounding sentence makes clear which direction is meant.
can name a person of faith caught in a moment of not trusting, not only someone permanently outside the faithJhn 20:27Mrk 9:19
Both
both point to a person who does not believe, and Paul does use the word for the class of people outside the community of faith1Co 6:6
Only unbeliever
the English noun frames the person as a settled religious category or identity, a fixed camp opposite the faithful, which the Greek does not always intend
Labels a person: the unbeliever, someone standing outside the faith, especially in Paul's contrast between the believer and the outsider.1Co 6:62Co 6:141Ti 5:8
Can also mean incredible, said of a claim too hard to credit rather than of a person's faith.Act 26:8
Both
Both name the failure or absence of faith and treat it as culpable, the opposite of trusting God.Mrk 16:14Jhn 20:27
Names unbelief as an abstract state or act, the inner condition of failing to trust that stalls God's work and forfeits his promises.Mat 13:58Heb 3:19Rom 11:20
Describes a condition a believer can wrestle with and be delivered from, not a fixed label on a person.Mrk 9:24Rom 4:201Ti 1:13
Names the plain absence of trust, and stands as the exact opposite of trusting. Jesus tells Thomas to stop being this and be the opposite (John 20:27), calls a whole generation this when they cannot rely on him (Matthew 17:17), and Paul says such minds have been blinded so the good news does not shine on them (2 Corinthians 4:4).Jhn 20:27Mat 17:172Co 4:4
It became the everyday label for people outside the church, used without heat in ordinary social situations: a husband who does not share his wife's faith (1 Corinthians 7:13), a neighbor who invites you to dinner (1 Corinthians 10:27), an outsider who wanders into a meeting and hears what is said (1 Corinthians 14:24).1Co 7:131Co 10:271Co 14:24
It can also face the other way, toward what cannot be trusted rather than toward someone who will not trust. Paul asks why his hearers judge it beyond belief that God raises the dead, where the word describes the claim itself (Acts 26:8), and the servant caught neglecting his master is put with a group many translations render "the unfaithful" (Luke 12:46).Act 26:8Luk 12:46
Both
Both name a settled failure toward God rather than a passing mood, and both turn up in lists of what marks a life apart from him: one among foolishness and being enslaved to cravings (Titus 3:3), the other among cowardice, corruption, and lying (Revelation 21:8).Tit 3:3Rev 21:8
Both work as a name for a whole class of people, so English Bibles can turn either into a group noun: those who will not be won over, whom John is sent to turn (Luke 1:17), and those who do not believe, who have no share with a believer (2 Corinthians 6:15).Luk 1:172Co 6:15
Points at a known claim the person will not comply with. Paul tells Agrippa he did not refuse the heavenly vision he had been given (Acts 26:19), and Titus describes people who say they know God yet contradict him by what they do (Titus 1:16). The problem is not that the claim is doubted, but that it is resisted.Act 26:19Tit 1:16
It is the word used for children who will not obey their parents, in lists of a society coming apart (Romans 1:30,2 Timothy 3:2). The refusal here is aimed at ordinary human authority, not at a religious claim at all.Rom 1:302Ti 3:2
Because the failure is an unwilling will rather than an unconvinced mind, the cure is described as being turned around: John's work is to turn such people toward the good sense of the righteous (Luke 1:17), and Paul groups the trait with being led astray by cravings rather than with doubt (Titus 3:3).Luk 1:17Tit 3:3
Used as a noun for a whole class of people, the unbelievers, those outside the faith as a settled group: an unbelieving spouse, unbelievers in court, at a shared table, or in the assembly.1Co 7:122Co 6:141Ti 5:81Co 6:6
Describes faithlessness as a fixed quality or character, a faithless generation or a person urged to stop being faithless.Mat 17:17Jhn 20:27Tit 1:15
Can turn passive to mean unbelievable or incredible, said of a claim rather than of a person, a shade the verb never carries.Act 26:8
Both
Both mark the absence of faith in God's message, the same fundamental non-response, whether named as an act of disbelief (the verb) or as a settled condition (the adjective).Mrk 16:162Co 4:4
Names the act of refusing to accept a report as true, above all the disciples disbelieving the news that Jesus was alive.Luk 24:11Mrk 16:11Luk 24:41Act 28:24
Carries a covenant sense of being unfaithful, breaking faith with God, set against the God who stays faithful even so.Rom 3:32Ti 2:13
Names what a person will not trust: God at work, the report of the risen Jesus, the promise itself. The complaint is about refusal to believe, not about a lack of schooling.Mat 17:17Mrk 9:19Jhn 20:27
Works as a settled label for the people outside the believing community, which is why it turns up in practical instructions about whom to marry, whose dinner invitation to accept, and whom to take to court.1Co 7:121Co 7:151Co 10:271Co 6:6
Carries a verdict. Those it names can be set opposite believers as a rival camp, blamed for a blinded mind, held up as the standard a neglectful Christian has fallen below, or listed among those facing judgment.2Co 6:142Co 4:41Ti 5:8Rev 21:8
Can describe a claim rather than a person, meaning "too much to be believed": Paul asks why the raising of the dead is judged incredible.Act 26:8
Both
Both name someone on the outside looking in, and Paul pairs them precisely because each is a visitor who walks into the gathering without the shared understanding the members have.1Co 14:23
Both serve as the test of whether what happens in the assembly can be understood: unintelligible speech makes the church look mad to them, while clear speech reaches and exposes them.1Co 14:231Co 14:24
The two words sit so closely together in this one passage, joined by "or" in both directions, that readers disagree over whether Paul is naming a single group of outsiders in two ways or two different kinds of visitor.1Co 14:241Co 14:23
Measures a person against training or expertise rather than against faith, so it can be said of committed believers: the council notices that Peter and John have had no formal schooling, and Paul concedes he is no trained speaker.Act 4:132Co 11:6
Carries no charge of guilt. Paul applies it to himself without apology, and Luke reports it as the observers' assessment of two men he plainly presents as faithful.2Co 11:6Act 4:13
Marks where someone stands relative to a group's own knowledge: the person who cannot follow the words being spoken and so cannot add an "Amen" to a prayer of thanks.1Co 14:16
Names a person who has no faith at all: the outsider who has not believed in Jesus. It is the standard New Testament label for those outside the church, set opposite the believer.1Co 6:62Co 6:141Co 7:12
Carries a hard, sometimes condemning edge. Their minds are blinded, and the lot of the faithless is named alongside murderers and idolaters in the lake of fire.2Co 4:4Rev 21:8
Used of a whole faithless generation that has refused to trust, a rebuke aimed at the unbelieving crowd rather than at a struggling follower.Mat 17:17Mrk 9:19
Both
Both fault a shortfall of trust and stand on the same scale of faith. One marks its total absence in the outsider, the other its weakness in the follower, so the two words sit at opposite ends of one line.Jhn 20:27Mat 14:31
Names a disciple who genuinely has faith, just not enough of it in the moment. The fault is a faith that runs short under pressure, not a faith that is absent.Mat 8:26Mat 14:31
Reserved for those already inside, Jesus' own followers. Every time it appears he is gently correcting people who are with him, never an outsider.Mat 6:30Mat 16:8Luk 12:28
What scholars say about apistos
The lexica treat ἄπιστος as the alpha-privative of πιστός, carrying both an active sense ("not believing, faithless") and a passive sense ("incredible, not to be believed"), a duality already present in classical and Hellenistic Greek (LSJ; BDAG). In the Gospels the active adjectival use predominates (the ἄπιστος γενεά of Matt 17:17 par.; the imperative to Thomas in John 20:27). In Paul the substantival οἱ ἄπιστοι functions as a near-technical designation for those outside the believing community (1 Cor 5-14; 2 Cor 4:4; 6:14-15), which Bultmann (TDNT 6:174-228, s.v. πιστεύω κτλ.) and the EDNT entry read as sociological boundary language rather than a comment on individual psychology. The passive sense "incredible" is confined to Acts 26:8 (ἄπιστον κρίνεται), where it qualifies the proposition of resurrection, not a person; Moulton-Milligan document the same passive usage in the papyri. 2 Cor 4:4 is debated by commentators (Thrall, Harris) as to whether ἀπίστων is the object or the beneficiary of the blinding, but the meaning of the word itself is not in question.
Sources
BDAG, s.v. ἄπιστοςlexicon
LSJ, s.v. ἄπιστοςlexicon
R. Bultmann, "πιστεύω κτλ.," TDNT 6:174-228theological-dictionary
EDNT, s.v. ἄπιστος, ἀπιστίαtheological-dictionary
J. H. Moulton and G. Milligan, The Vocabulary of the Greek Testament, s.v. ἄπιστοςlexicon
A. C. Thiselton, The First Epistle to the Corinthians (NIGTC)commentary