Subjuntivo presente: cambios vocálicos

Stem-changing verbs in the present subjunctive follow two patterns at once: a base pattern inherited from the present indicative (the "boot"), and — for one specific subclass — an extra stem change that does not appear in the indicative at all. Get the base pattern wrong and you sound like an A1 learner; get the extra wrinkle wrong and you sound like a B1 learner who knows the rule but has not heard enough Spanish to feel where it applies. This page is the difference between B1 and B2 for one narrow but very high-frequency corner of the language.

The base pattern: -ar and -er stem-changers wear the boot

For -ar and -er verbs that stem-change in the present indicative (pensar → pienso, volver → vuelvo, querer → quiero), the present subjunctive follows the same rule: the stem changes in every person except nosotros and vosotros. Visualised on a conjugation table, the persons that change form the shape of a boot, with the heel at nosotros/vosotros and the upper at the other four persons.

The reason the boot exists, in both the indicative and the subjunctive, is purely phonological: the stem vowel diphthongises (e → ie, o → ue) only when it is stressed. In piense the stress falls on the e of the stem, so it diphthongises to ie. In pensemos the stress falls on the ending (-MOS), leaving the stem vowel unstressed and undiphthongised. Same rule in the subjunctive as in the indicative — once you have the boot, you have it everywhere.

The wrinkle: -ir stem-changers change in nosotros and vosotros too

This is the rule that catches B1 learners by surprise. -Ir verbs that stem-change in the present indicative (sentir, dormir, pedir, morir, preferir, servir) carry a stem change in the subjunctive even in nosotros and vosotros — the two persons that stay regular in the indicative.

The change in nosotros/vosotros is not the same as the change in the boot persons. It is the second, "weak" stem change that -ir verbs alone display: e → i (not ie), and o → u (not ue). Same pattern that shows up in the third-person preterite (sintió, durmió) and the gerund (sintiendo, durmiendo).

Look closely at the sentir column. Four persons show ie (the boot persons), but nosotros and vosotros show i (sintamos, sintáis), not e (sentamos, sentáis) and not ie (sientamos, sientáis). All three would be wrong; only sintamos / sintáis is correct.

The same pattern applies to dormir: yo duerma, tú duermas, but nosotros durmamos, vosotros durmáis — never dormamos (no change) or duermamos (wrong change).

For pedir (and other e>i verbs like servir, repetir, seguir, vestir), the picture is simpler because there is only one stem change to track: the e becomes i in all six persons of the subjunctive, since pedir already does e>i (not e>ie) in the indicative boot. So nosotros pidamos and vosotros pidáis fall right into line.

Why -ir verbs are different: the historical explanation

The reason -ir verbs carry the extra change in nosotros/vosotros has to do with a Latin sound change that affected the high vowel i differently from the mid vowels e and o. Old Spanish -ir verbs (descended from Latin -ire verbs) had a stem vowel that was already "weak" in unstressed position, and the language regularised this weakness across the entire subjunctive paradigm — including the persons where the indicative leaves the vowel alone.

For learners, the takeaway is simple: the subjunctive of an -ir stem-changer is harder than the indicative. The indicative gives you the boot; the subjunctive gives you the boot plus a vowel-reduction in the two persons that the boot exempts. There is no logical shortcut for -ar or -er verbs to anticipate this; you have to learn the -ir class as its own pattern.

A complete reference table

Here is a side-by-side table of the most common stem-changing verbs in the present subjunctive, showing every person.

A few notes on this table.

Jugar is the only u>ue verb in Spanish. The g/gu spelling shift (juguemos, juguéis) happens to keep the hard /g/ sound before the front vowel e — this is a spelling change, not a separate stem change.

Seguir drops the silent u before a in siga, sigas, siga, sigamos, sigáis, sigan — segu- would be misread, so the spelling change preserves the pronunciation /siga/.

Reír is a small but high-frequency irregularity: its stem is ri- throughout the subjunctive, but the written forms can be tricky (ría has an accent on í because of hiatus; riais drops the accent because the diphthong ia is short and the stress falls naturally on it).

The peninsular vosotros — full inventory

Spain's vosotros form is where the -ir wrinkle becomes most useful to practise, because it is the form English-language teaching skips most often. Here is the full set of subjunctive vosotros forms for the verbs that commonly trip learners up:

The bolded forms are the ones that surprise learners: they are the only place in the entire Spanish verb system where a vosotros form gets a stem change that the indicative version did not have.

Common mistakes

These are the recurring errors learners make with stem-changing verbs in the present subjunctive.

✅ No quiero que muráis de aburrimiento.

Correct: morir → muráis in subjunctive vosotros.

Key takeaways

• -Ar and -er stem-changers follow the boot: the stem changes in yo, tú, él, ellos; nosotros and vosotros stay regular.
• -Ir stem-changers wear the boot plus a weak change (e>i, o>u) in nosotros and vosotros — this is the rule that separates B1 from B2.
• Pensar → pensemos / penséis (no diphthong, boot exempt).
• Sentir → sintamos / sintáis (weak change applies).
• Dormir → durmamos / durmáis (weak change applies).
• Pedir, servir, seguir and other e>i verbs are simpler — the change applies in all six persons.
• The peninsular vosotros forms are where this rule becomes most useful: durmáis, sintáis, prefiráis are the markers that signal you have actually internalised the system rather than just memorised the indicative.