se + Pluperfect Subjunctive + Conditional Perfect

This structure is used for counterfactual past events—things that did not occur.

1. The Structure:

• The 'If' Clause: se + Pretérito Mais-que-Perfeito do Subjuntivo (tivesse auxiliary + Past Participle). Note the required written accent on the nós forms (e.g., tivéssemos, houvéssemos).
• The Result Clause: Condicional Composto (teria auxiliary + Past Participle).
• Punctuation: Use a comma when the Se clause comes first. Do not use a comma when the result clause comes first (e.g., Eu teria avisado se eu tivesse sabido).
• Mixed Conditionals: If the hypothetical past event affects the present, the result clause uses the simple conditional instead (e.g., Se eu tivesse estudado, eu estaria pronto agora - If I had studied, I would be ready now).
• Note: The past participle in these compound tenses is always invariable (e.g., elas tivessem chegado). In formal or literary contexts, the auxiliary verb haver can be used instead of ter (e.g., se houvesse feito, haveria feito).

2. Formal vs. Colloquial:
While the Condicional Composto (teria feito) is the standard for writing, the Mais-que-Perfeito Composto do Indicativo (tinha feito) is the dominant spoken preference in European Portuguese. In Brazilian Portuguese, speakers use a mix of teria feito, the simple Pretérito Imperfeito (fazia), the Pretérito Imperfeito of ir + infinitive (ia fazer), or the colloquial ia ter + past participle (ia ter feito). Additionally, in colloquial speech, native speakers frequently substitute the simple Imperfect Subjunctive for the Pluperfect Subjunctive in the 'if' clause (e.g., using Se eu soubesse instead of Se eu tivesse sabido). However, this substitution is considered a grammatical error in formal writing because se eu soubesse strictly refers to a present unreal condition ('If I knew').
Examples:
EP preference: 'Se eu tivesse visto, tinha dito' (If I had seen it, I would have said it).
General colloquial (Imperfect): 'Se eu soubesse, eu avisava' (If I had known, I would have warned you).
BP colloquial (ia ter + particípio): 'Se eu tivesse visto, eu ia ter dito' (If I had seen it, I would have said it).

3. Clitic Placement:
In European Portuguese, the se clause attracts pronouns (proclisis): Se me tivesse dito.... In the result clause, formal EP requires mesoclisis with the conditional. Note that mesoclisis in compound tenses applies exclusively to the auxiliary verb, never the past participle (e.g., ter-me-ia dito, not teria-me dito or teria dito-me), unless a negative word or other attractor forces proclisis (não me teria dito). In colloquial speech using the 'tinha' replacement, enclisis is used: tinha-me dito. In Brazilian Portuguese, proclisis is standard in the result clause as well (e.g., ele me teria avisado or ele teria me avisado).

4. Journalistic Usage (Unconfirmed Events):
Outside of 'if' clauses, the Condicional Composto is frequently used in news reports to indicate unconfirmed past events, rumors, or allegations (e.g., O suspeito teria fugido - The suspect reportedly fled).