There are 3 categories of stem changing "boot" verbs:

• o --» ue (also jugar, oler)
• e --» ie
• e --» i   (only w/ IR verbs)

The preterite sometimes requires a spelling change in the yo form to preserve the sound.

• c --» qu
• g --» gu

There is also an orthographic change that happens like this (no sound change, just a tradition).

• z --» c

There are several irregular preterite stems. Here are some of them:

In the preterite 3rd person, as well as the present participle (iendo), IR verbs will see a 1/2 stem change:

• o --» u
• e --» i
• e --» i

Also, Old McDonald had a farm...e i e i o. So whenever you see any of those triple combinations, remember to change the i to y. This also goes for traer even those it's not an Old McDonald.

There is no stem-changing in the imperfect.

And there are only THREE irregular verbs.

Ir:  iba
Ser: era
Ver:  veía

There is no real need to dilineate the conjugations for IR verbs apart from ER verbs outside of the present tense. The preterite is presented above only to show the 3rd person 1/2 stem change. The imperfect is given only to keep with the convention of this page.

Normally for the future and the conditional you add these endings to the infinitive (as opposed to the stem) of the verb. However, there is a set of verbs with irregular stems, which you should memorize.