The irregular stem-changing preterite

All the verbs other than "ir"/"ser" and -IR verbs that stem change in the present tense shown in this Contraseña section actually belong to the same verb family.

• This family of verbs are ones who show profound and irregular changes to their stems in the preterite forms, and those profound changes are present throughout the conjugation (even nosotros-forms).

• The trick to being successful with these verbs is two-fold:
• 1. Get all the irregular stems memorized.
• 2. Memorize the cohort of endings that is used with this verb family (which is different from all other sets of preterite endings). 

Let's begin by memorizing what I call the "u-stem" verbs.

• These verbs are:
• estar
• tener
• poder

• Why do I call them u-stems? Because in the preterite their stems change to:
• estuv 
• tuv
• pud
   
• Don't worry about why this is so--just memorize that these are the preterite stems you need.

Next, let's memorize what I call the "i-stem" verbs.

• These verbs are:
• querer
• venir
• hacer

• Why call them i-stems? Because in the preterite their stems change to:
• quis
• vin
• hic (the stem for the 3rd-person singular form is "hiz"--more on that later)
   
• Again, the whole trick here is just to learn that these are the preterite stems you need (and memorization is the best way to do that).

Now let's learn what I call the "inverted stem" verbs.

• These verbs are:
• saber
• poner

• Why call them inverted stems? Because in the preterite their stems change to inverses of each other:
• sup
• pus
   
• Again, your job is to learn that these are the preterite stems you need for these 2 verbs. 

To end, we need to deal with what I call the "j-stem" verbs.

• These verbs are:
• decir--this is featured in Unidad 10 in Contraseña
   
• Other verbs do this, too (just FYI, no need to memorize them): 
• traer
• conducir
• traducir
   
• Why call them j-stems? Because in the preterite their stems change to:
• dij
• Just FYI, those other verbs' stems are traj, conduj, traduj
   
• NOTE: As we will see on the next slide, this sub-family has a different 3rd-person-plural ending than the rest of the irregular stem-changing preterite verbs.

To conjugate all these verbs in the preterite, do this:

• 1. Write your irregular stem.
• 2. Add the appropriate ending to that stem for the subject.

What are our irregular-stem-changing preterite endings? Good question. They are:

• For subject yo: "e" (NO accent mark)
   
• For subject tú: "iste"
   
• For 3rd-person-singular subject: "o" (NO accent mark)
   
• For subject nosotros: "imos"
   
• For 3rd-person-plural subject for all verbs except J-stems: ieron
• For 3rd-person plural subject for J-stem verbs: eron

Let's see some of these verbs fully conjugated (we'll look at "hacer" separately on the next slide):

U-stem verb: estar

Irregular stem: estuv

Conjugated forms:

• yo estuve
• tú estuviste
• él/ella/Ud. estuvo
• nosotros estuvimos
• ellos/ellas/Uds. estuvieron

I-stem verb: querer

Irregular stem: quis

Conjugated forms:

• yo quise
• tú quisiste
• él/ella/Ud. quiso
• nosotros quisimos
• ellos/ellas/Uds. quisieron

J-stem verb: decir

Irregular stem: dij

Conjugated forms:

• yo dije

• tú dijiste
• él/ella/Ud. dijo
• nosotros dijimos
• ellos/ellas/Uds. dijeron

We will look at I-stem irregular preterite verb "hacer" separately because of a spelling change it has in its 3rd-person singular form:

I-stem verb: hacer

Irregular stem: hic (with one exception)

Conjugated forms:

• yo hice
• tú hiciste
• él/ella/Ud. hiZo
• nosotros hicimos
• ellos/ellas/Uds. hicieron

Lastly, and on a completely different subject, we have the profoundly irregular preterite of the verbs "ir" and "ser". (I don't know why your Contraseña insists on conflating things that are not the same.)

"Ir" and "ser" have the exact same forms in the preterite. This never causes confusion, by the way.

These forms must be memorized. They cannot be created through derivation.

They are: 

• yo fui
• tú fuiste
• él/ella/Ud. fue
• nosotros fuimos
• ellos/ellas/Uds. fueron