comenzar

Comenzar — "to begin, to start" — combines two of Spanish's most common irregularities into a single verb. First, it is an e>ie stem-changing verb (like cerrar, pensar, querer): the root vowel diphthongizes whenever stress falls on it. Second, it is a -zar verb, which means z must shift to c whenever the next letter would be e — Spanish does not write ze in native words. The two changes operate independently and combine cleanly: you might see the diphthong, the spelling shift, both, or neither, depending on the form. Once you can predict where each one applies, comenzar (and its cousins empezar, almorzar, organizar, tropezar) becomes entirely systematic.

In everyday Spain, empezar is somewhat more common in conversation; comenzar sounds a notch more formal or careful, and dominates in writing, journalism, and any setting where speech is composed rather than spontaneous. The two are otherwise interchangeable in meaning.

Non-finite forms

The gerundio and participio show neither change: the root is unstressed (no diphthong) and the next letter is not e (no spelling shift).

Indicative — simple tenses

Presente — diphthong in the "boot"

The classic "1-2-3-6" pattern: diphthong wherever the root vowel is stressed, plain e in nosotros and vosotros where stress moves to the ending. The z stays z throughout because no ending here starts with e.

Pretérito perfecto simple — spelling shift in yo

The first-person singular comencé — the ending -é would force a written ze, which Spanish does not allow. So z shifts to c. Every other person in the preterite keeps z because the endings start with a or o. There is no diphthong in the preterite: -ar stem-changing verbs only show the diphthong in the present.

Pretérito imperfecto

No diphthong, no spelling shift — endings start with a, root vowel unstressed.

Futuro simple

Condicional

Indicative — compound tenses

All compound tenses pair haber with the regular participle comenzado.

Pretérito perfecto compuesto

Pretérito pluscuamperfecto

Futuro compuesto

Condicional compuesto

Subjunctive — simple tenses

Presente de subjuntivo — both changes apply

This is the form where both irregularities meet. The endings (-e, -es, -e, -emos, -éis, -en) all start with e — so z shifts to c across the whole paradigm. The boot pattern still applies for the diphthong: stressed root → ie, unstressed root → e.

Read carefully: every form has c (because every ending starts with e), but only four forms have the diphthong (the boot).

Imperfecto de subjuntivo (-ra / -se)

No diphthong (root unstressed), no spelling shift (endings start with -ar-). The -ra set dominates in spoken Spain; -se is more formal or literary.

Subjunctive — compound tenses

Pretérito perfecto de subjuntivo

Pluscuamperfecto de subjuntivo

Imperative

The imperative mixes both changes again. Tú and vosotros affirmatives are built from forms that take neither change in their respective slots (comienza: diphthong but no c; comenzad: neither). The negative imperative and the usted/nosotros/ustedes forms all draw from the subjunctive, so they apply both irregularities.

Look closely at the vosotros row. The affirmative comenzad keeps z (the ending -ad starts with a) and shows no diphthong (stress on the ending). The negative no comencéis takes c (ending -éis starts with e) but still no diphthong. This is the kind of detail learners often get wrong — and where careful reasoning from first principles pays off.

When pronouns attach to an affirmative imperative, write them as one word and add a written accent if needed: comiénzalo, comenzadlo, comencémoslo. The spelling shift travels with the form — comencémoslo keeps the c because it began as comencemos.

Comenzar a + infinitive

By far the most common syntactic frame for comenzar is comenzar a + infinitive — "to begin to do something." The a is non-negotiable: dropping it is one of the most frequent learner errors.

You can also say comenzar con algo — "to start with something" — for an opening item, theme, or step.

Comenzar vs. empezar

In meaning, the two verbs are interchangeable. The differences are register and frequency.

Mechanically they conjugate identically (both are e>ie and -zar), so learning one teaches you the other.

High-frequency collocations from peninsular Spanish

Reflexive use: comenzarse

The reflexive comenzarse exists but is rare and largely formal or literary. In everyday Spain you say la reunión comienza a las cinco, not se comienza. Reserve comenzarse for passive-like uses in writing.

The classic English-speaker error

English uses "start" with a bare infinitive or a gerund: "I started to study" or "I started studying." Neither maps cleanly to Spanish. Comenzar (and empezar) require a + infinitive — no gerund, no bare infinitive.

Common Mistakes

Key Takeaways

• Comenzar combines two changes: e>ie stem-change (when the root is stressed) and -zar spelling shift (z → c before e).
• The diphthong appears in the present indicative and subjunctive "boot" (yo, tú, él, ellos) — never in nosotros or vosotros.
• The z → c shift appears wherever the next letter would be e: comencé (1st pers. preterite) and the entire present subjunctive (comience, comiences, comencemos, comencéis, ...).
• The vosotros affirmative imperative is comenzad; the negative is no comencéis.
• The standard syntactic frame is comenzar a + infinitive — never with a gerund, never with a bare infinitive.
• In Spain empezar dominates everyday speech; comenzar is the slightly more formal synonym, common in writing and careful registers.
• Once comenzar is mastered, the same combined logic gives you empezar, tropezar, almorzar, organizar and other e>ie
  • -zar verbs.