To be honest, primary school was long ago and I can't remember if I was taught any rule. I know when to use "s" or "z" from everyday usage, I presume.

  • we use an "s" in such verbs as atrasar, alisar, analisar, avisar, pesquisar, paralisar, arrasar, extravasar, frisar, etc.

  • and a "z" is used in agonizar, amenizar, batizar, concretizar, simpatizar, utilizar, realizar, civilizar, etc.

For those who are learning Portuguese as a foreign language, this must be a hard nut to crack. Is there any rule to make things easier for the student?


Verbs that end in -sar are derived from nouns whose last syllable has already an "s", if that syllable is preserved in the transition to the verbal variation. Otherwise, the -zar form will be used.

The examples you mention are quite illustrative:

atrasar/atraso, alisar/(a)liso, analisar/análise, avisar/aviso, pesquisar/pesquisa, paralisar/parálise(paralisia), arrasar/(ar)raso, extravasar/(extra)vaso, frisar/friso.

agonizar/agonia, amenizar/ameno, batizar/batismo, concretizar/concreto, simpatizar/simpatia, utilizar/útil, realizar/real, civilizar/civil.

  • Very interesting. If you could provide links, your answer would be a great contribution to our site.
    – Centaurus
    Aug 23 '15 at 23:39
  • 2
    All the sources I found didn't say anything about the origin of this rule. It may come from usage, from norm, or both. In any case, the logic behind it probably has to do with the history of the phoneme [z] in Portuguese. As I understand it, most words where "s" is used with a [z] sound were originally pronounced with an [s] sound, but kept being written as before, causing the confusion. Aug 24 '15 at 1:03
  • 1
    Interestingly, analizar is an obsolete spelling of analisar.
    – tchrist
    Aug 26 '15 at 0:21
  • He's right. But some words like catequizar is from "catechizare" and not catequese. So it's not as simple like always. Jan 22 '18 at 2:35
  • 1
    Yes, the sounds are the same. One of those situations where spelling is not determined by phonetics alone. Jan 22 '18 at 20:57

Eu prefiro explicar desta maneira: não se trata de -zar, mas de -izar, uma derivação comum na morfologia das línguas românicas (e nas que têm essa origem no Inglês e no Alemão) que em Português implica sempre o z. Os exemplos dados por André Sousa Lemos ilustram todos essa regra. No restante, trata-se de derivar com -ar, não com -sar.

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