The past subjunctive expresses a possibility, perhaps already realized, depending on a verb in the present or future tense:
- Credo che tu abbia letto questo libro.
- I believe you have read this book.
- Immmaginerà che tu sia andata via.
- He will imagine that you have gone away.
The past perfect subjunctive expresses a possibility that was not realized depending on a verb in the past tense:
- Credevo che tu avessi già letto questo libro.
- I thought you had already read this book.
1. The form of the past subjunctive.
The past subjunctive is formed with the present subjunctive of the auxiliary verbs [essere (to be) and avere (to have)], and the past participle of the verb.
[The present subjunctive of essere and avere + P.P]
| Person | Capire (to understand) | Arrivare (to arrive) |
| io tu lui/lei noi voi loro | abbia capito abbia capito abbia capito abbiamo capito abbiate capito abbiano capito | sia arrivato/arrivata sia arrivato/arrivata sia arrivato/arrivata siamo arrivati/arrivate siate arrivati/arrivate siano arrivati/arrivate |
The past subjunctive of the verb avere is avere and that of essere is essere.
2. The form of the past perfect subjunctive.
The past perfect subjunctive is formed with the imperfect of the auxiliary verbs [essere (to be) and avere (to have)], and the past participle of the verb.
[The imperfect subjunctive of essere and avere + P.P]
| Person | Capire (to understand) | Arrivare (to arrive) |
| io tu lui/lei noi voi loro | avessi capito avessi capito avesse capito avessimo capito aveste capito avessero capito | fossi arrivato/arrivata fossi arrivato/arrivata fosse arrivato/arrivata fossimo arrivati/arrivate foste arrivati/arrivate fossero arrivati/arrivate |
The subjunctive past perfect of the verb avere is avere and that of essere is essere.