Spanish 26 - Irregularities in plural nouns

Until now we've learned two rules for making a Spanish noun plural:

  1. If the noun ends in a vowel, add -s
  2. If the noun ends in a consonant, add -es

The second rule has some exceptions, which are summed up below.

If the noun ends in a z, drop the z and add -ces

el lápiz
the pencil
los lápices
the pencils

If the noun ends in an s or an x, add -es only if the stress is on the last syllable (which is always the case in monosyllabic words). Otherwise, add nothing.

el alisis
the analysis
los análisis
the analyses
el país
the country
los países
the countries
el fax
the fax
los faxes
the faxes
el torax
the thorax
los torax
the thoraxes

And finally, if the noun has an accent mark on the last syllable, we remove the accent mark if that doesn't influence its pronunciation.

el avión
the plane
los aviones
the planes

This is because the stress is on the second last syllable by default, so here aviones retains the stress on on even though we drop the accent mark. Note that in países we didn't drop the accent mark, since this would have changed the pronuncation, because without the accent mark país would have been pronounced as one syllable instead of two.