The formation of the Ud. and Uds. commands

The formation of the Ud. and Uds. commands

The formal commands (Ud. and Uds.) are based on the yo-form of the present indicative. First, take off the final -o. Then, add either -a or -an for verbs ending in -er and -ir, or -e or -en, for verbs ending in -ar. For example, note the following transformations from the infinitive, through the yo-form of the present indicative, to the Ud. and Uds. command forms:

present tense yo-form
Ud. command form
Uds. command form

hablar
hablo
hable
hablen

comer
como
coma
coman

vivir
vivo
viva
vivan

Note that this holds for almost all verbs, including all those verbs that had an irregular stem in the present tense as well as stem-vowel changing verbs (e-to ie, e to i, and o to ue):

present tense yo-form
Ud. command form
Uds. command form

pensar
pienso
piense
piensen

dormir
duermo
duerma
duerman

pedir
pido
pida
pidan

hacer
hago
haga
hagan

tener
tengo
tenga
tengan

decir
digo
diga
digan

salir
salgo
salga
salgan

In some cases, Spanish spelling conventions cause a slight change in spelling. These are not true irregular forms because their pronunciation follows all the rules. But if one change the o to e after c or g, one must spell the resulting syllable que or gue in order to keep the sound soft. Likewise, zo changes to ce and (and vice-versa):

present tense yo-form
Ud. command form
Uds. command form

buscar
busco
busque
busquen

pagar
pago
pague
paguen

empezar
empiezo
empiece
empiecen

Finally, there are a few verbs whose Ud. and Uds. command forms do not follow these rules. In general, they are those verbs whose yo-forms in the present end in a y: doy, estoy, voy, soy, plus haber and saber:

present tense yo-form
Ud. command form
Uds. command form

dar
doy
dé
den

estoy
estoy
esté
estén

ir
voy
vaya
vayan

ser
soy
sea
sean

haber
he
haya
hayan

saber
sé
sepa
sepan