In short

You now know how to build both past tenses: the pretérito perfeito simples of Lessons 20-21 (comi, fui, disse) and the pretérito imperfeito of Lesson 22 (comia, ia, dizia). The hard part is not forming them - it is choosing between them, because English uses one shape, the plain past (“ate”, “went”, “said”), for both. Portuguese splits that single English past into two jobs. The perfeito simples reports an event: something that happened and finished, a step that moves the story forward. The imperfeito paints the frame around events: what things were like, what used to happen, and what was going on. A typical past sentence needs both at once - Quando cheguei, estava a chover (“When I arrived, it was raining”): the arrival is perfeito, the rain is imperfeito. Get that division of labour right and your Portuguese past stops sounding translated.

The rule

The core opposition: event vs frame

Ask one question of every past verb: is this a single finished event, or the background around events?

• Perfeito simples = the camera clicks. A completed, bounded action, however long it lasted, seen as one whole: Ontem li um livro (“Yesterday I read a book” - start to finish). It answers “what happened (next)?”.
• Imperfeito = the camera pans. An ongoing state, a description, a habit, or an action still in progress, with no eye on where it ends: Naquele tempo lia muito (“Back then I used to read a lot”). It answers “what was it like?” or “what was going on?”.

The two work as a team. In a story, the imperfeito holds the scene still and the perfeito delivers the events that happen against it:

• Estava sol e as pessoas passeavam quando, de repente, um cão atravessou a estrada.
  • It was sunny and people were strolling when, suddenly, a dog crossed the road.
• The weather (estava), the strolling (passeavam) are the frame - imperfeito. The dog crossing (atravessou) is the event - perfeito.

The two English tests

Because English hides the split, translate it back into these two shapes:

1. If you can reword the English as “used to X” or “was Xing”, use the imperfeito.
2. If it is a single “X-ed, and that was that” - one finished event, often with “then”, “suddenly”, “finally” - use the perfeito simples.

• Every summer we went to Faro = “used to go” -> íamos (imperfeito, habit).
• That summer we went to Faro = one trip, done -> fomos (perfeito, event).

The interruption pattern

The commonest place both tenses meet in one sentence: a longer action in progress (imperfeito) is cut across by a completed event (perfeito).

• Eu dormia quando o alarme tocou. - I was sleeping when the alarm went off.
• O que fazias quando te telefonei? - What were you doing when I called you?

The background can be the plain imperfeito (dormia) or, for extra stress on “in the act of”, the estava a + infinitivo frame of Lesson 9 in the imperfeito (estava a dormir); either way, the interrupting event stays perfeito.

Sequence vs simultaneity

• A chain of completed events = perfeito after perfeito. Each verb pushes the story on:
  • Entrei, sentei-me e pedi um café. - I went in, sat down and ordered a coffee.
• Two ongoing actions side by side = imperfeito with enquanto (“while”):
  • Enquanto ela cozinhava, eu punha a mesa. - While she cooked, I set the table.

Same verb, two tenses, two meanings

A small group of very common verbs shift meaning with the tense - the imperfeito gives the ongoing state, the perfeito the moment it changed. These are worth memorising as pairs:

• Eu já a conhecia, mas só ontem soube o nome dela. - I already knew her, but only yesterday did I find out her name.
• Ele não quis assinar. - He refused to sign. (a decision, not a lingering wish)

Words that tip you off

Certain time expressions almost always call one tense:

• Perfeito (a point or a closed stretch): ontem, no ano passado, de repente, então, finalmente, uma vez, durante três anos. A counted, closed period is still perfeito: Vivi em Lisboa cinco anos (“I lived in Lisbon for five years” - and no longer).
• Imperfeito (repetition or no boundary): sempre, normalmente, todos os dias, às vezes, antigamente, naquele tempo, enquanto.

Forms & patterns

A decision table for the past verb in front of you:

The very same verb can flip: começar is perfeito when it names one moment (começou às nove) but imperfeito as a habit (começava sempre tarde, “it always used to start late”).

Examples

Common mistakes

• A casa foi grande e teve um jardim -> A casa era grande e tinha um jardim - a past description is the imperfeito, never the perfeito.
• Todos os dias comprei pão (a habit) -> Todos os dias comprava pão - “used to” is the imperfeito; comprei means “I bought (once)”.
• Ontem lia um livro (meaning “I read one, finished”) -> Ontem li um livro - a single completed event is the perfeito; lia would mean “was reading / used to read”.
• Eu conhecia o Rui na festa -> Eu conheci o Rui na festa - meeting someone for the first time is the event conheci; conhecia means you already knew him.
• Sabia a notícia ontem for “I found out” -> Soube a notícia ontem - the moment of learning is soube; sabia is the ongoing “already knew”.
• Quando cheguei, chovia wrongly “fixed” to choveu -> keep chovia - the rain is the frame around your arrival, not a new event; the arrival (cheguei) is the perfeito.

Tips

• Do the English test first, then choose: “used to / was -ing” -> imperfeito; “did once, done” -> perfeito. It resolves the great majority of cases before you touch the endings.
• Think of a film: the imperfeito is the set (weather, mood, setting); the perfeito is each action that advances the plot. A narrative alternates between the two.
• Length does not decide it: Estudei dez anos is still perfeito, one closed block. What counts is whether the action is seen as finished/bounded (perfeito) or open/ongoing (imperfeito).
• Memorise the meaning-shift pairs (sabia/soube, conhecia/conheci, queria/quis, podia/pude, tinha/teve); English speakers lose the most marks here, because English keeps the same word for both.
• Joined by quando, the usual split is imperfeito (background) + perfeito (event): Jantávamos quando eles chegaram. Swap the tenses and the meaning changes, so check which verb is the frame.