sei vs ser, What's the Difference?

Which to use

“sei” is a num and “ser” is a verb - they look or sound alike but fill different roles in a sentence.

#48,072
“sei” frequency rank: #39
“ser” frequency rank: 48111
confusion score

Side-by-Side Comparison

Feature	sei	ser
Definition	Seis.	Tener algo una determinada naturaleza, propiedad o cualidad estable.

Where the eye mixes sei and ser

Muted = shared; highlighted = the visual trap. They share 2 letters in sequence.

3 ch

sei

3 ch

ser

Look-alike desk: sei vs ser

These two trip readers on the page rather than in the ear: sei is /s̺ej/ while ser is [ˈseɾ]. Spoken aloud the problem disappears. In writing it persists, because they differ by a single letter - i in “sei” becomes r in “ser”, and the parts of speech differ too (num vs verb), which is usually the fastest check. Our composite confusion score for this pair is 48111, derived from the frequency rank of both members and their visual similarity.

sei is recorded at frequency rank #48,072, classified as anum, pronounced /s̺ej/. ser is at rank #39, tagged as averb, pronounced [ˈseɾ].

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 48111, this pair ranks #116,273 of 323,831 scored Spanish confusable pairs - roughly mid-pack for confusability.

Orthographic DNA of sei vs ser

Shared letters: es. Private to "sei": i. Private to "ser": r.

"sei" · 3 letters · shape CVV · "ser" · 3 letters · shape CVC

Frequently Asked Questions

Is swapping "sei" for "ser" ever safe?

No - they are not even the same part of speech. "sei" is a num and "ser" a verb, so a sentence built for one is usually ungrammatical with the other.

Frequency check: "sei" vs "ser" - which ranks higher?

"ser" is the more common of the two: it sits at frequency rank #39 in our Spanish list, against #48,072 for "sei". That is a wide gap, so in ordinary text the rarer spelling is the one worth double-checking.

After this comparison

Eye-level mix-up between "sei" and "ser" is sorted above. Next: full entries or other pairs that share a letter shape.

Full dictionary entry for "sei" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "ser" - compare definitions side by side with the headword page. Word entry
This pair ranks #116,273 of 323,831 scored Spanish confusable pairs in this corpus vintage. Corpus statistics
"sei" and "ser" also get mixed up with nearby pairs, the highest-scored neighbour is "sei vs stem". Nearby pair

Confusion rank #116,273 of 323,831 scored Spanish pairs, corpus vintage 2026-09-03, not spelling advice.