You guys have done several great lessons about the grammar behind the preterite and imperfect tenses. The grammar rules seem straight forward, but I still have an incredibly difficult time trying to figure out when to use one or the other.
Sometimes it's very clear when to use each one, but on the whole I'm still struggling trying to master these two tenses.
If you all could come up with some type of lesson, forum post or anything that would really help to clarify when to choose one over the other, it would be great. I just can't seem to work things out with just the grammar rules alone.
It not an easy distinction to make, so don't feel bad. I want to continue to think about how else to help you differentiate these two...
Here's one way to look at it which I don't think we've taught yet. The imperfect of the indicative can often be replaced by the absolute preterit indicative + gerund.
For example: "hablaba con Martín por dos horas" can also be phrased "estuve hablando con Martín por dos horas". Notice how the gerund accounts for the sense of duration which is implicit in the imperfect mood. Again, "trabajaba todo el día" can likewise be said "estuve trabajando todo el día".
In English, we use the preterit and gerund "I was talking", "I was working", and I hope that this makes it easier to link the idea of duration to the imperfect. For now, it may be useful to learn how to form it and then just keep your eyes open for instances of it. When you find an example of it, try to ask yourself what the time is that's expressed by it.