Spanish Preterite Tense

Regular Verbs

100

I ran

Corrí

200

He lived

vivió

300

They spoke

hablaron

400

You wrote

escribiste or escribió

500

Y'all sang

Cantaron or Cantasteis

Irregular Verbs

100

You (informal) went

fuiste

200

They were

fueron

300

I gave

di

400

We saw

vimos

500

y'all (Spain) saw

visteis

Stem-Changers

100

he asked for

pidió

200

they preferred

prefirieron

300

She slept

durmió

400

he competed 

compitió

500

They died 

murieron 

Irregular Stem Verbs

100

I walked

anduve

200

We were (estar)

estuvimos

300

they came

vinieron

400

I brought

traje

500

they did

hicieron

-car, -gar, -zar verbs

100

I played

jugué

200

I searched for

busqué

300

You (informal) at lunch 

almorzó

400

I ate lunch

almorcé

500

Why is there a spelling change in the yo form of these verbs?

In order for the conjugated form to sound like the infinitive, the spelling must change slightly.