In Spanish there are two forms that can be used where in English you would use the past progressive tense "was/were +ing".
Which form you need depends on the timeframe of the ongoing action in the past.
1. El Imperfecto progresivo
We use the Imperfecto progresivo in these cases:
- When the ongoing action is simply describing "what was happening" without any emphasis or implication about start or end time (see the first three examples above).
- When it is combined with another action that interrupts the ongoing action at that time. The interrupting action is generally in the simple past (see the last example where the ongoing action "She was washing her hair" was interrupted by another sudden action "he arrived".
2. El Indefinido progresivo
We use the Indefinido progresivo in this case:
- When the ongoing past action is inside a completed timeframe in the past. See how all examples above contain a time phrase: "toda la noche", "de 6 a 7 de la tarde", "el sábado pasado".
Bear in mind that the Imperfecto progresivo, when it is used to describe a scene purely in the past, can very often be interchangeable with the Imperfecto. For example:
- Estaba lloviendo y la gente estaba corriendo para protegerse de la lluvia. (Imperfecto progresivo)
- Llovía y la gente corría para protegerse de la lluvia. (Imperfecto)
(It was raining and people were running for cover from the rain.)
Sometimes the timeframe isn't specific about having a beginning and an end so you may find this type of sentences using El Indefinido Progresivo [estuve+gerund]
We don't know when the "eating" started, but the end is expressed with "hasta que nos acabamos toda la comida". This may sound as if that is an interrupting action and may lead you to wrongly think you need to use El Imperfecto Progresivo [estaba+gerund].
Remember that some gerunds are irregular. See:
- List of Spanish Irregular Gerunds of the form -yendo
- List of Spanish Irregular Gerunds of the form -iendo