Where the manuscripts differ · Matthew 17:21
Prayer and fasting — a verse that is missing from Matthew
Matthew's verse 21 — "this kind goeth not out but by prayer and fasting" — is absent from the earliest manuscripts and looks like a copy of Mark 9:29 that a scribe wrote into the margin.
Open an older Bible to Matthew 17 and you will find verse 21. Open a newer one and the numbers jump straight from 20 to 22, sometimes with a footnote at the bottom of the page. Nothing has been deleted from your Bible; the number was assigned in the 1500s to a text that later turned out to be missing from the oldest copies, and modern editions keep the gap in the numbering so the verse references everyone already uses still line up.
The words themselves are not in question anywhere else. Jesus really does say something almost identical in Mark 9:29, and every manuscript of Mark has it. The question is only whether Matthew wrote it too, or whether a scribe who knew Mark by heart supplied it here.
This is the single most common kind of variant in the New Testament, and it has a name: harmonization. Copyists knew the Gospels well, and when one Gospel told a story more fully than another, the fuller version had a way of migrating over.
What the manuscripts actually show
| Witness | Date | What it reads here |
|---|---|---|
| Codex Sinaiticus and Codex Vaticanus | 4th century | No verse 21 at all — the text runs straight from verse 20 to verse 22. |
| The Byzantine majority of Greek manuscripts | 9th–15th centuries | "Howbeit this kind goeth not out save by prayer and fasting." This is the reading behind the KJV. |
| Old Latin and Syriac witnesses | 4th–7th centuries | Mixed — some carry the sentence, some do not. |
| Mark 9:29 in the earliest manuscripts | 4th century and earlier | "This kind can come forth by nothing, but by prayer" — with the words "and fasting" themselves added by many later copies. The extra phrase grew in Mark before it appeared in Matthew. |
The case each way
That it belongs in the text
The sentence is in the great majority of surviving Greek manuscripts, and it is old enough to appear in early translations, so it is not a late medieval invention.
Matthew and Mark are telling the same story, and there is no reason in principle why Jesus could not have been quoted the same way by both.
An argument from omission has to explain the omission. If the words were original, a copyist's eye could have skipped a line, though this is easier to assert than to demonstrate here.
That it came later
The oldest complete Greek Bibles simply do not have it, and they are not the only witnesses that lack it.
The wording in the manuscripts that do have it matches Mark closely — which is what a borrowed sentence looks like, and not what two independent writers usually produce.
Copyists demonstrably added to Matthew from Mark and Luke far more often than they cut. In textual criticism the reading that explains the others usually wins, and 'a scribe brought Mark's line over' explains everything here.
The phrase "and fasting" was itself still growing in Mark's text during the same centuries. Watching a phrase expand in one Gospel while appearing in another is strong evidence for what happened.