So, what is a stem and how exactly do these verbs change?
A stem is the part of the verb that comes before the ending (which, in infinitive verbs, is always either ar, er, or ir). In regular conjugations, the stem doesn’t change, where in irregular conjugations, it can be completely different. In stem-changing verbs, the change is in the last vowel of the stem.
Stem-changing verbs in Spanish can also be thought of as 1, 2, 3, 6 verbs. This is because in the traditional conjugation tables, the conjugations that change are the first, second, third and sixth.
Let’s see that visualized.
Stem-changing verbs in Spanish: affected conjugations
1yoI2túyou3usted, él, ellayou (formal), he, she4nosotroswe5vosotrosplural you (informal)6ustedes, ellos, ellasplural you (formal), they
In other words, the affected conjugations are in singular, the first person (yo), the second person (tú) and second person formal (usted), the third person (él, ella), and in plural, the second person formal (ustedes), and the third person (ellos, ellas).
It might be easier to think of it as the ones that are not affected as there are fewer: just nosotros and vosotros. In case you were wondering about vos, it is also unaffected. These are conjugated just as they are when it’s a regular verb.
There are a few different ways that stem-changing verbs in Spanish can change. The key is in the vowels in the verb. Let’s see the different possibilities:
e -> ie (e.g: pensar)
e -> i (eg: conseguir)
o -> ue (eg: encontrar)
others (i -> ie, u -> ue)
Stem-changing verbs where the e in the stem changes to ie
In the Spanish stem-changing verbs where e conjugates into ie, the last e of the stem turns into ie in the present tense conjugations 1, 2, 3, and 6.
Examples:
1. Pensar | to think
Breakdown:
Pens – ar
Stem: pens
Stem change: e -> ie – pens -> piens
Pensar conjugation
1yopienso2túpiensas3usted, él, ellapiensa4nosotrospensamos5vosotrospensáis6ustedes, ellos, ellaspiensan
2. Preferir | to prefer
Stem change: prefer -> prefier
Note that the stem changes in the same way no matter whether the verb ends in ar, er, or ir.
Preferir conjugation
1yoprefiero2túprefieres3usted, él, ellaprefiere4nosotrospreferimos5vosotrospreferís6ustedes, ellos, ellasprefieren
3. Entender | to understand
Stem change: entend -> entiend
Entender conjugation
1yoentiendo2túentiendes3usted, él, ellaentiende4nosotrosentendemos5vosotrosentendéis6ustedes, ellos, ellasentienden
4. Empezar | to start
Stem change: empez -> empiez
Note that the change is always on the last syllable of the stem, no matter how many other vowels there are in the verb.
Empezar conjugation
1yoempiezo2túempiezas3usted, él, ellaempieza4nosotrosempezamos5vosotrosempezáis6ustedes, ellos, ellasempiezan
Stem-changing verbs where the e in the stem changes to i
These are similar to the verbs above, except instead of ie, the vowel in the last syllable of the stem just changes to i in the first, second, third and sixth. This type of stem-changing verb tends to be ir-ending verbs only.
Examples:
1. Conseguir | to obtain
Breakdown:
Conseg – (u)ir
Note: the u before the i is there to show that the g in the word is pronounced as a hard g. So this is not considered part of the stem. Some would say that this makes conseguir irregular in the present first person, but since it is caused by a straightforward spelling rule, I wouldn’t consider it as such.
Stem: conseg
Stem change: e -> i – conseg -> consig
Conseguir conjugation
1yoconsigo2túconsigues3usted, él, ellaconsigue4nosotrosconseguimos5vosotrosconeguís6ustedes, ellos, ellasconsiguen
2. Servir | to serve
Stem change: serv -> sirv
Servir conjugation
1yosirvo2túsirves3usted, él, ellasirve4nosotrosservimos5vosotrosservís6ustedes, ellos, ellassirven
Stem-changing verbs where the o in the stem changes to ue
Again, once you understand the rules, this is a pretty straightforward vowel change.
Examples:
1. Almorzar | to have lunch
Breakdown:
Almorz – ar
Stem: almorz
Stem change: o -> ue – almorz -> almuerz
Almorzar conjugation
1yoalmuerzo2túalmuerzas3usted, él, ellaalmuerza4nosotrosalmorzamos5vosotrosalmorzáis6ustedes, ellos, ellasalmuerzan
2. Encontrar | to find
Stem change: econtr -> encuentr
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