El Presente de Subjuntivo

The present subjuntive forms are based on the yo form of the present tense. If the form ends in -o, remove it and replace it with the "opposite" vowel(for -ar verbs = e, for -er and -ir verb = a) + -s, -mos, -is and -n for tú, nosotros, vosotros, and ustedes/ ellos/ ellas:
 
ending in -ar ending in -er or in -ir
hablar comer vivir
yo habl e com a viv a
tú habl es com as viv as
él, ella, Ud.  habl e com a viv a
nosotros/ as  habl emos com amos viv amos
vosotros/ as  habl éis com áis viv áis
ellos, ellas, Uds.  habl en com an viv an

It is important to use the first person present, the "yo -form", because if it is irregular, the subjunctive forms are also irregular.
 

Note that for verbs that end in -gar, and -car you have to change the writing from -g- to -gu-, and -c- to -qu- (to show that g still sounds like [g] and c sounds like [k]. (Remember that g before e is pronounced [x] (like in México), and c before e is pronounced [s].). Verbs that end in -zar have a change from z to c.

Examples: 

llegar:      llegue, llegues, llegue, lleguemos, lleguéis, lleguen
buscar:     busque, busques, busque, busquemos, busquéis, busquen
empezar:  empiece, empieces, empiece, empecemos, empecéis, empiecen

Vowel-changing verbs

If an -ar or -er verb has a spelling change in the first person present indicative, the present subjunctive will have the same changes, except in the first and second person plural (like the regular present forms) :
 
pensar querer contar mover
yo piens e quier a cuent e muev a
tú piens es quier as cuent es muev as
él, ella, Ud.  piens e quier a cuent e muev a
nosotros/ as  pens emos quer amos cont emos mov emos
vosotros/ as  pens éis quer áis cont éis mov áis
ellos, ellas, Uds.  piens en quier an cuent en muev an
ojo2.gif - 639 BytesIn the first and second person plural forms of stem-changing-ir verbs, the eof the stem changes to i, and the ochanges to u
pedir sentir dormir
yo pid a sient a duerm a
tú pid as sient as duerm as
él, ella, Ud.  pid a sient a duerm a
nosotros/ as  pid amos sint amos durm amos
vosotros/ as  pid áis sint áis durm áis
ellos, ellas, Uds.  pid an sient an duerm an

Irregular verbs

If the first person singular of a verb in the present indicative is irregular, the present subjunctive will show the same irregularity:
 
decir hacer
yo dig a hag  a
tú dig as hag as
él, ella, Ud.  dig a hag a
nosotros/ as  dig amos hag amos
vosotros/ as  dig áis hag áis
ellos, ellas, Uds.  dig an hag an

The subjunctive stems of the following irregular verbs must be memorized because here it is not possible to apply the above mentioned rule to use the first person present indicative and to drop the "o" because their first person present does not end in "o" :
 

dar estar haber saber ser ir
yo d é est é hay a sep a se a vay a
tú d es est és hay as sep as se as vay as
él, ella, Ud.  d é est é hay a sep a se a vay a
nosotros/ as  d emos est emos hay amos sep amos se amos vay amos
vosotros/ as  d eis est éis hay áis sep áis se áis vay áis
ellos, ellas, Uds.  d en est én hay an sep an se an vay an