Why do we classify "ser" as an irregular verb?

The Spanish Irregular Verbs are those verbs whose "raíces" or stems, change when they are conjugated in different tenses and with different personal pronouns. Unlike most –er and –ir verbs we’ve learned, tener and venir are both irregular verbs. In other words, their verb endings do not follow the ordinary pattern for verbs with their infinitive endings.

There are two types of irregular verbs in Spanish:

The ones that have a change in their vocal form: Contar - Cuento / Perder - Pierdo

The ones that have a change in their consonant consonant: Deducir - Deduzco / Enloquecer - Enloquezco

Why Complicate Things? The Role of Irregular Verbs in Spanish

Why do irregular verbs exist in Spanish? Just as in English, irregular verbs have evolved as a result of spoken usage and ease of pronunciation. For example, compare the sounds of the word teno with the word tengo. The second word sounds cleaner and clearer, doesn’t it?  

If tener was a regular verb, its “yo” form would be “teno.” But it’s not. Look at the verb endings for venir and tener in the following table:

Subject

TENER

VENIR

Yo

ten-go

ven-go

Tú

tien-es

vien-es

Ud., él, ella

tien-e

vien-e

Nosotros/as

ten-emos

ven-imos

Vosotros/as

ten-éis

ven-ís

Uds., ellos, ellas

tien-en

vien-en

The irregularity of the verbs occurs in two areas.

1. The “yo” form is completely irregular, with a ‘g’ added before the –o ending.

2. The stem of the verbs changes in the tú, Ud., and Uds. forms. The “e” is replaced by “ie”.  

Try saying the word tene. Now say tiene. Can you hear why the stem changes?

Por ejemplo:

Tú vienes de Brasil, ¿verdad?

You come from Brazil, right?

No, yo vengo de Argentina.

No, I come from Argentina.

¿Tienen Ustedes familia en España?

Do you have family in Spain?

Sí, nosotros tenemos familia en España.

Yes, we have family in Spain.

Using TENER to Talk about Age, What You Have, Whether You’re Hungry, and What You Feel Like Doing.

The verb “tener” is extremely common in Spanish. A mastery of it will enable you to say everything from how old you are to whether you’re cold or thirsty.

In its most basic meaning, tener means “to have.” For example, “Tengo un trabajo,” means I have a job. If you want to say that you have to do something, you will use tener que. For example, “Tengo que ir al mercado,” means I have to go to the market.  

Tener is also used in the colloquial phrase, “I feel like…” If you want to say you feel like doing something, start your sentence with, “Tengo ganas de…”