In short

The present subjunctive (Lesson 33) covers wishes, doubts and emotions anchored in the present or future: Espero que venhas. The pretérito imperfeito do conjuntivo is its past-and-hypothetical twin. You reach for it in three everyday situations: when the same trigger sits in a past or conditional clause (Queria que viesses - “I’d like you to come”), when you build an unreal-present “if” (Se eu tivesse tempo, ia contigo - “If I had time, I’d go with you”), and after como se (“as if”). It is also the tense inside the fixed wish quem me dera (“if only…”). The good news: you do not memorise a new irregular list. This tense is built mechanically from a form you already produced in Lessons 20-21 - the eles/elas preterite - so if you can say foram, tiveram, fizeram, you can build every form here.

The rule

How to build it: from the eles-form of the preterite

Take the 3rd person plural of the pretérito perfeito simples (the eles/elas form, Lessons 20-21), remove the ending -ram, and add one set of endings to what is left:

• -sse, -sses, -sse, -ssemos, -ssem

The stem you get this way is the same for regular and irregular verbs, which is why the irregulars cost you nothing extra. One spelling point: the nós form always carries a written accent on the vowel just before -ssemos (falássemos, comêssemos, fôssemos).

Regular verbs

Full pattern for falar: falasse, falasses, falasse, falássemos, falassem.

Irregular verbs: same trick, irregular stem

Because the preterite stem is irregular, so is this tense - but you already learned those preterites, so just chop -ram and add the endings:

When you use it

1. A subjunctive trigger in the past or conditional. Every trigger from Lessons 34-36 (wish, emotion, influence, doubt, impersonal expressions) demands the present subjunctive when the main verb is present, and the imperfect subjunctive when the main verb is past or conditional. The tenses simply shift back together:

• Quero que venhas -> Queria que viesses. (I want you to come -> I wanted / would like you to come.)
• É importante que ele saiba -> Era importante que ele soubesse.
• Duvido que seja verdade -> Duvidava que fosse verdade.

2. Unreal present (“second conditional”). For a situation contrary to fact now, use se + imperfect subjunctive in the if-clause, and the imperfeito or the conditional (Lesson 32) in the result:

• Se eu tivesse dinheiro, comprava / compraria uma casa. - If I had money, I’d buy a house.
• Se fosses mais cedo, apanhavas o comboio. - If you left earlier, you’d catch the train.

Portuguese, unlike English, never puts the conditional after se: the se-clause takes the subjunctive, the result clause takes the conditional or imperfeito. The full three-type system is Lesson 49; this is the middle one.

3. como se (“as if”) always takes the imperfect (or pluperfect) subjunctive, because the comparison is unreal:

• Ele fala como se soubesse tudo. - He talks as if he knew everything.
• Trata-me como se fosse uma criança. - He treats me as if I were a child.

4. Wishes: quem me dera. The fixed exclamative quem me dera (“if only…”, literally “who would give me”) takes an infinitive or que + imperfect subjunctive:

• Quem me dera saber cantar! - I wish I could sing!
• Quem me dera que fosse verdade. - If only it were true.

5. A relative clause about something not yet identified. When the noun is only being looked for, imagined or denied - not a particular one you could point at - the relative clause (que, onde, cujo, or quem with no antecedent at all) goes into the subjunctive, the imperfect one after a past or conditional main verb:

• Queríamos um hotel que aceitasse animais. - we had not found one. Contrast Ficámos no hotel que aceitava animais - that one exists, so the indicative stays.
• Não existia nenhum voo que chegasse antes das dez. - a negated antecedent works the same way.

Forms & patterns

The endings, added to the eles-preterite stem (after dropping -ram):

Trigger-tense agreement, at a glance:

Examples

Common mistakes

• Queria que tu venhas -> Queria que tu viesses - a past or conditional main verb pulls the subjunctive back to the imperfect; the present subjunctive clashes with queria.
• Se eu tinha dinheiro, comprava… -> Se eu tivesse dinheiro, comprava… - an unreal-present if takes the imperfect subjunctive, not the indicative imperfeito.
• Se eu seria rico… / Se eu teria tempo… -> Se eu fosse rico / Se eu tivesse tempo - never put the conditional after se; the se-clause is subjunctive.
• que ele fazesse / que ele podesse -> que ele fizesse / pudesse - build the stem from the eles-preterite (fizeram, puderam), not from the infinitive.
• que nós fossemos -> que nós fôssemos - the nós form needs the written accent before -ssemos (fôssemos, tivéssemos, falássemos).
• Ele fala como se sabe tudo -> como se soubesse tudo - como se always governs the imperfect subjunctive, never the indicative.
• Quem me dera que é verdade -> Quem me dera que fosse verdade - quem me dera is a wish, so it takes the imperfect subjunctive.

Tips

• The one shortcut that gives you the whole tense: say the eles/elas preterite (foram, tiveram, fizeram, disseram, puderam), drop -ram, add -sse. No separate irregular table to learn.
• Match the tenses across the sentence: present trigger -> present subjunctive, past or conditional trigger -> imperfect subjunctive. Quero que venhas / Queria que viesses.
• For an unreal present, both halves step back: se + imperfect subjunctive, then imperfeito or conditional in the result (Se pudesse, ia / iria contigo). The complete conditional-type system is Lesson 49.
• Burn in the rule that surprises English and Spanish speakers less but trips beginners: no conditional and no future after se. The se-clause is always subjunctive here.
• Learn quem me dera as a ready-made way to say “I wish / if only”: Quem me dera saber (+ infinitive) or Quem me dera que ficasses (+ imperfect subjunctive). Oxalá also takes the imperfect subjunctive for an unlikely wish, but directly, with no que and no infinitive (Oxalá fosse verdade).
• Always accent the nós form: falássemos, comêssemos, partíssemos, fôssemos, tivéssemos, fizéssemos.
• Brazilian Portuguese uses exactly the same forms and the same uses for this tense; the only real EP/BP gap in these sentences is clitic placement (Lesson 30), not the subjunctive itself.