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):

	CONVENCER (present indicative)	CONVENCER (present subjunctive)
yo	convenzo	convenza
tú	convences	convenzas
él / ella / usted	convence	convenza
nosotros / nosotras	convencemos	convenzamos
vosotros / vosotras	convencéis	convenzáis
ellos / ellas/ ustedes	convencen	convenzan