IMPERFECT

conocía       I knew, I was acquainted with

costaba       it cost (before purchasing)

podía           I could, was able to (I was in a position to)

no podía     I was not able to, could not

quería         I wanted to, desired to

no quería     I didn't want to

sabía            I knew, knew ho to, had knowledge that

tenía             I had (in my possession)

tenía que      I had to (but did not necessarily do it)

* Sometimes the preterites of these verbs retain their original meanings

Siempre supe que ibas a triunfar  

PRETERITE

conocí        I met, made the acquaintance of

costó           it cost (after purchasing)

pude            I was able to (and did)

no pude       I tried (but couldn't)

quise            I tried to

no quise       I refused, would not

supe             I learned, found out

tuve              I had, received

tuve que       I had to (and did do it)

I always knew that you were going to succeed.

No conocía a Miguel; lo conocí ayer en el Internet.

I didn't know Miguel; I met him yesterday on the Internet.

Carmen no quiso comprar las entradas, porque costaban mucho.

Carmen refused to buy the tickets because they cost too much.

No pude venir el lunes a clase porque tuve que acompañar a mi madre al médico

I couldn't come to class on Monday because I had to accompany my mother to the doctor

Compré los libros que tenía que comprar, pero me costaron $160 

I bought the books I had to buy  (was supposed to buy), but they cost me $160