Verbos con cambio ortográfico c>z (presente subjuntivo)

Stem-changing Spanish c>z verbs in the present subjunctive)

In Spanish some verbs ending in -cer/-cir undergo a stem change in the present subjunctive, in a very similar way they do in the present indicative. They will switch the -c for a -z The difference is that while in the present indicative only the yo form is affected by this stem change, in the present subjunctive all forms keep the stem change.
Have a look at these tables showing both the present indicative and the present subjunctive of convencer (to convince):

(present indicative)
(present subjunctive)
 yo convenzo convenza
  convences convenzas

él / ella / usted

convence convenza
nosotros / nosotras convencemos convenzamos
vosotros / vosotras convencéis convenzáis
ellos / ellas/ ustedes convencen convenzan
Let me take a look at that...