Present Stem Changes 1

Some Spanish verbs are called stem-changing verbs. They still use the normal present tense endings, but the stem changes in certain forms.

What is a stem?

The stem is the part of the verb that remains after removing -ar, -er, or -ir.

• pensar → pens-
• comenzar → comenz-
• entender → entend-

In some verbs, a vowel inside that stem changes when the verb is conjugated.

Where stem changes happen

In the present tense, these changes affect:

• yo
• tú
• él / ella / usted
• ellos / ellas / ustedes

They do not affect:

• nosotros / nosotras
• vosotros / vosotras

This is called the boot verb pattern (or shoe verb pattern) because the changed forms make a boot shape in the conjugation chart.

Why nosotros and vosotros stay different

These forms have stress in a different part of the word. Because of that, the stem remains unchanged.

Compare:

• pienso, piensas, piensa — stress falls on the stem
• pensamos, pensáis — stress falls after the stem

Why these verbs matter

These verbs are very common and useful. The endings stay regular — only the stem changes. That means:

• You still use regular present endings (-o, -as, -a, -amos, -áis, -an for -AR)
• Only the stem vowel changes in the boot forms

Stem-Changing Verbs: Overview

In Stem Changes 1, you learn that some present tense verbs are semi-irregular. They still use regular endings, but the stem vowel changes in the boot forms.

Three Patterns in This Level

1. e → ie — the most common stem change 2. u → ú — accent addition in -UAR verbs 3. i → í — accent addition in -IAR verbs

Pattern 1: e → ie

The vowel e inside the stem changes to ie in yo, tú, él/ella/usted, and ellos/ellas/ustedes.

Full Conjugation: pensar (to think)

Common e → ie verbs

The e → ie pattern appears in all three verb groups (-AR, -ER, -IR).

Pattern 2: u → ú (accent addition)

In many verbs ending in -UAR, the u receives an accent in the boot forms.

Full Conjugation: continuar (to continue)

Common -UAR verbs: continuar, actuar, situar, graduar, evaluar, efectuar

Pattern 3: i → í (accent addition)

In many verbs ending in -IAR, the i receives an accent in the boot forms.

Full Conjugation: enviar (to send)

Common -IAR verbs: enviar, confiar, variar, ampliar, guiar, criar

Important: Not every verb ending in -iar or -uar takes an accent. These must be learned by pattern.

Compare: Regular vs Stem-Changing

The endings are identical! Only the stem changes.

Quick Rule Summary

e → ie: Change the e in the stem to ie in boot forms (yo, tú, él/ella, ellos/ellas).

u → ú: In many -UAR verbs, the u takes an accent in boot forms.

i → í: In many -IAR verbs, the i takes an accent in boot forms.

Learning Strategy

Do not treat every verb as an isolated case. Look for:

• Repeated vowel changes
• Families of similar verbs (empezar / comenzar, sentir / preferir / mentir)
• Shared patterns like -entir, -erir, -iar, -uar

Quick Pattern Check