iff vs IJ, What's the Difference?

Which to use

“iff” is a conjunction and “IJ” is a name - they look or sound alike but fill different roles in a sentence.

#45,443
“iff” frequency rank: #46,535
“IJ” frequency rank: 91978
confusion score

Side-by-Side Comparison

Feature	iff	IJ
Definition	Abbreviation of if and only if.	A lake (formerly a bay) adjoining the city of Amsterdam, Netherlands.

Where the spellings diverge

Shared letters are muted; the letters that actually set iff and IJ apart are highlighted. They share 1 letter in sequence, which is exactly why the eye skips the difference.

3 ch

iff

2 ch

Spelling & Dictionary Insight

These two trip readers on the page rather than in the ear: iff is /ɪf ən(d)ˈəʊn.li ɪf/ while IJ is /eɪ/. Spoken aloud the problem disappears. In writing it persists, because they differ by 1 letter(s) in length, and the parts of speech differ too (conjunction vs name), which is usually the fastest check. Our composite confusion score for this pair is 91978, 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/. IJ is at rank #46,535, tagged as aname, pronounced /eɪ/.

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 91978, this pair ranks #2,933 of 530,003 scored English confusable pairs - among the most confusable pairs.

Orthographic DNA of iff vs IJ

Shared letters: i. Private to "iff": f. Private to "IJ": j.

"iff" · 3 letters · shape VCC · "IJ" · 2 letters · shape VC

Frequency comparison

iff#45,443

IJ#46,535

Source: FrequencyWords open word-frequency list

Frequently Asked Questions

Can "iff" and "IJ" be used interchangeably?

No - they are not even the same part of speech. "iff" is a conjunction and "IJ" a name, so a sentence built for one is usually ungrammatical with the other.

Which is more common, "iff" or "IJ"?

"iff" is the more common of the two: it sits at frequency rank #45,443 in our English list, against #46,535 for "IJ". The two are close in frequency, so neither is a safe default; check the meaning rather than guessing.

Remembering iff vs IJ

The fastest way to pick the right one every time.

Check the role first: if you need a conjunction, it's “iff”; for a name, it's “IJ”.
See each word in full, definition, IPA, etymology and its other confusables. Full “iff” entry
Browse more pairs most likely to be confused. Most confusable