Pretérito Imperfecto – what the hell is it?

Right now I’m wrestling with the following grammar problem. In one of the Nivel Inicial exams I’ve come across the sentences below:

Qué animal había en casa de la chica?
Tenía un gato cuando era un nino.

What’s that? Of course during the exam I had no idea what that was so after checking the scores I got back to the grammar theory and I found out that the verb forms relate to past. But…. in Spanish, just like in English there’s no single past tense.

The one with forms like había and tenía is called pretérito imperfecto or copretérito. It is used to describe background activities (like the sun was shining (background) when I got married (foreground, main action). You can also use it for actions that you did it in the past with some regularity just like in English you’d use I used to. You could say then that we use pretérito imperfecto for actions that haven’t been completed in the past. It’s interesting to see that English and Spanish tenses don’t overlap, isn’t it?

Ok, so here’s how they conjugate the verb in pretérito imperfecto:

verbs ending with -ar (hablar)
yo hablaba
tú hablabas
el hablaba

nosotros hablábamos
vosostros hablabais
ellos hablaban

verbs ending with -er (tener) or -ir (vivir)
yo tenía, vivía
tú tenías, vivías
el tenía, vivía

nosotros teníamos, vivíamos
vosotros teníais, vivíais
ellos tenían, vivían

So, where’s the catch? Where’s the exception?
ir
yo iba
tú ibas
el iba

nosotros íbamos
vosotros ibais
ellos iban

ser
yo era
tú eras
el era

nosotros éramos
vosotros erais
ellos eran

ver
yo veía
tú veías
el veía

nosotros veíamos
vosotros veíais
ellos veían

And that’s it. When I learn these, I’ll write some tasks how to master them.