sem vs si, What's the Difference?

Which to use

“sem” is a preposition and “si” is a pronoun - they look or sound alike but fill different roles in a sentence.

#69
“sem” frequency rank: #482
“si” frequency rank: 551
confusion score

Side-by-Side Comparison

Feature	sem	si
Definition	indicativa de carência ou ausência	refere-se à terceira pessoa, indica reflexividade e é usado após preposição (a, de, em, contra, sobre, por, etc., exceto com)

Where the eye mixes sem and si

Muted = shared; highlighted = the visual trap. They share 1 letter in sequence.

3 ch

sem

2 ch

Look-alike desk: sem vs si

These two trip readers on the page rather than in the ear: sem is /sɐ̃j̃/ while si is /ˈsi/. 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 (preposition vs pronoun), which is usually the fastest check. Our composite confusion score for this pair is 551, derived from the frequency rank of both members and their visual similarity.

sem is recorded at frequency rank #69, classified as aprep, pronounced /sɐ̃j̃/. si is at rank #482, tagged as apron, pronounced /ˈsi/.

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 551, this pair ranks #75,120 of 75,631 scored Portuguese confusable pairs - a relatively easy-to-tell-apart pair.

Orthographic DNA of sem vs si

Shared letters: s. Private to "sem": em. Private to "si": i.

"sem" · 3 letters · shape CVC · "si" · 2 letters · shape CV

Frequently Asked Questions

Is swapping "sem" for "si" ever safe?

No - they are not even the same part of speech. "sem" is a preposition and "si" a pronoun, so a sentence built for one is usually ungrammatical with the other.

In ordinary Portuguese text, does "sem" or "si" show up more?

"sem" is the more common of the two: it sits at frequency rank #69 in our Portuguese list, against #482 for "si". The two are close in frequency, so neither is a safe default; check the meaning rather than guessing.

Useful next steps

Visual near-miss handled. Browse the word pages or a neighbour when the next look-alike shows up.

Full dictionary entry for "sem" with definition, IPA, and generated misspellings. Word entry
Full dictionary entry for "si" - compare definitions side by side with the headword page. Word entry
This pair ranks #75,120 of 75,631 scored Portuguese confusable pairs in this corpus vintage. Corpus statistics
"sem" and "si" also get mixed up with nearby pairs, the highest-scored neighbour is "Sau vs si". Nearby pair

Confusion rank #75,120 of 75,631 scored Portuguese pairs, corpus vintage 2026-09-03, not spelling advice.