Stem-changing Spanish i>y verbs in the present subjunctiveIn Spanish some verbs ending in -uir undergo a stem change in the present subjunctive, in a very similar way they do in the present indicative. They will switch the -i for -y. The difference is that while in the present indicative the nosotros and vosotros forms do not change, in the present subjunctive all forms are affected by this change.
Have a look at these tables showing both the present indicative and the present subjunctive of construir (to build):
él / ella / usted
|nosotros / nosotras||construimos||construyamos|
|vosotros / vosotras||construís||construyáis|
|ellos / ellas/ ustedes||construyen||construyan|