sevssiWhat's the difference?

Quick tell: se is a conjunction, si is a pronoun, so they fill different roles in a sentence.

Which to use

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

#16
“se” frequency rank
#482
“si” frequency rank
498
confusion score

Side-by-Side Comparison

Feature se si
Definition indica hipótese 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 se and si

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

2 ch
se
2 ch
si

Spelling & Dictionary Insight

These two trip readers on the page rather than in the ear: se is /sɨ/ while si is /ˈsi/. Spoken aloud the problem disappears. In writing it persists, because they differ by a single letter - e in “se” becomes i in “si”, and the parts of speech differ too (conjunction vs pronoun), which is usually the fastest check. Our composite confusion score for this pair is 498, derived from the frequency rank of both members and their visual similarity.

se is recorded at frequency rank #16, classified as aconj, pronounced /sɨ/. 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 498, this pair ranks #75,165 of 75,631 scored Portuguese confusable pairs - a relatively easy-to-tell-apart pair.

Orthographic DNA of se vs si

Shared letters: s. Private to "se": e. Private to "si": i.

"se" · 2 letters · shape CV  ·  "si" · 2 letters · shape CV

Frequently Asked Questions

Can "se" and "si" be used interchangeably?
No - they are not even the same part of speech. "se" is a conjunction and "si" a pronoun, so a sentence built for one is usually ungrammatical with the other.
Which is more common, "se" or "si"?
"se" is the more common of the two: it sits at frequency rank #16 in our Portuguese list, against #482 for "si". That is a wide gap, so in ordinary text the rarer spelling is the one worth double-checking.

Source: Wiktionary (via kaikki.org) Structured Wiktionary extract

Source: FrequencyWords open word-frequency list