The Present Indicative in Spanish

The present indicative is the most commonly used tense but also the one that contains the most exceptions. That's the way it is and you will need to learn many verbs by heart. That being said, in the regular case, the present indicative is formed from the stem to which the following endings are added:
- verbs in -ar: -o, -as, -a, -amos, -áis, -an
- verbs in -er: -o, -es, -e, -emos, -éis, -en
- verbs in -ir: -o, -es, -e, -imos, -ís, -en

Irregular Verbs

As always in Spanish, irregularities involve a modification of the stem or a change in stress with possibly a spelling change.

1) First person in -go

Let's start with the -go forms. Indeed, a g appears in the conjugation in the first person only of certain verbs after an n, l or s: pongo (poner), tengo (tener), vengo (venir), valer (valgo), salgo (salir), asgo (asir).
We also have an -ig in the following verbs: caigo (caer), traigo (traer), oigo (oír)

Note that this form is also found in the present subjunctive: que yo salga. The rest of the conjugation is normal.

2) First person in -oy

Still in the first person, the following forms are irregular: soy (ser), estoy (estar), voy (ir), doy (dar). We say that a yod appears. Note that the conjugation of these verbs is generally irregular in the other persons of the present indicative and should be learned. For haber, we finally note the form hay.

3) First person with zc

The consonant c changes to zc in the first person: conozco (conocer), lucir (luzco), nazco (nacer).

4) Other irregular first persons

Finally, the first persons of these verbs are completely irregular: quepo (caber), he (haber), sé (saber), veo (ver).

5) The diphthong

Many verbs have a diphthong in the present indicative. Concretely, the three singular persons as well as the third person plural have a spelling modification to maintain a soft sound. Here are the main types of diphthongs:

6) Stem weakening

Verbs following the same pattern as pedir have a weakening of the stem vowel in the three singular persons as well as the third person plural. This is then found throughout the conjugation: pido, pides, pide, pedimos, pedís, piden (pedir)

7) Introduction of a y

Verbs ending in -uir see a y appear before an a, e or o. This is to maintain a soft sound. This occurs in the three singular persons as well as the third person plural: influyo, influyes, influye, influimos, influís, influyen (influir).