Which to use
“iff” is a conjunction and “ith” is an adjective - they look or sound alike but fill different roles in a sentence.
- #45,443
- “iff” frequency rank
- #49,435
- “ith” frequency rank
- 94878
- confusion score
Side-by-Side Comparison
| Feature | iff | ith |
|---|---|---|
| Definition | Abbreviation of if and only if. | Occurring at position i in a sequence. |
Where the eye mixes iff and ith
Muted = shared; highlighted = the visual trap. They share 1 letter in sequence. iff and ith follow the identical consonant-vowel pattern (VCC). Same shape at a glance is often the real trap, independent of shared letters.
Why the eye confuses iff with ith
These two trip readers on the page rather than in the ear: iff is /ɪf ən(d)ˈəʊn.li ɪf/ while ith is /aɪθ/. Spoken aloud the problem disappears. In writing it persists, because they share most of their letters but differ in 2 positions, and the parts of speech differ too (conjunction vs adjective), which is usually the fastest check. Our composite confusion score for this pair is 94878, derived from the frequency rank of both members and their visual similarity.
iff is recorded at frequency rank #45,443, classified as aconj, pronounced /ɪf ən(d)ˈəʊn.li ɪf/. ith is at rank #49,435, tagged as anadj, pronounced /aɪθ/.
Glosses for this pair are partially populated in our dataset, but the full side-by-side definitions above should still guide you to the right choice.
With a confusion score of 94878, this pair ranks #1,202 of 530,003 scored English confusable pairs - among the most confusable pairs.
Orthographic DNA of iff vs ith
Shared letters: i. Private to "iff": f. Private to "ith": ht.
"iff" · 3 letters · shape VCC · "ith" · 3 letters · shape VCC
Frequently Asked Questions
Can "iff" and "ith" be used interchangeably?
Which is more common, "iff" or "ith"?
After this comparison
Eye-level mix-up between "iff" and "ith" is sorted above. Next: full entries or other pairs that share a letter shape.
- Full dictionary entry for "iff" with definition, IPA, and generated misspellings. Word entry
- Full dictionary entry for "ith" - compare definitions side by side with the headword page. Word entry
- This pair ranks #1,202 of 530,003 scored English confusable pairs in this corpus vintage. Corpus statistics
- "iff" and "ith" also get mixed up with nearby pairs, the highest-scored neighbour is "ISR vs ith". Nearby pair
Confusion rank #1,202 of 530,003 scored English pairs, corpus vintage 2026-09-03, not spelling advice.