In short

The present subjunctive swaps the vowels you know: -are verbs take -i (lui parli), -ere/-ire verbs take -a (lui prenda, lui dorma). The first three persons are identical, so the subject pronoun becomes obligatory: penso che tu parli. Bonus: you get the polite Lei command free, because it is the very same form - Scusi!, Senta!, Mi dica!

The rule

This lesson is about forms only. When Italian forces you into the subjunctive - after penso che, spero che, è possibile che and their friends - is the whole subject of the next step; the past, imperfect and pluperfect subjunctive wait at step 43. Here you learn to build the forms, and you learn them once, because the Lei imperative is not a second thing to memorise - it is this same paradigm wearing a hat.

Step 1 - start from the io form of the present indicative, not from the infinitive. This is the trick that makes the subjunctive cheap. Take io in the present, drop the final -o, and add the subjunctive vowel. It works for regular verbs and, crucially, for almost every irregular one: vengo -> venga, faccio -> faccia, vado -> vada, posso -> possa, voglio -> voglia, dico -> dica, esco -> esca.

Step 2 - add -i for -are verbs, -a for everything else. The two vowels trade places with the indicative, which is exactly why it feels strange at first: lui parla (indicative) becomes lui parli; lui prende becomes lui prenda. If you catch yourself thinking “that ending belongs to the other conjugation”, you are doing it right.

Step 3 - the same form covers io, tu and lui/lei. All three are parli. Italian solves the resulting ambiguity by putting the pronoun back in: Penso che tu parli troppo and Penso che lui parli troppo are told apart by tu and lui alone. Dropping the pronoun here - a habit you built at step 4 - genuinely loses information, so the pronoun is not optional. The noi, voi and loro forms stay distinct and need no pronoun.

Step 4 - noi is free, voi is always -iate, loro is the singular + -no. The noi form is identical to the indicative (parliamo, prendiamo). The voi form always ends in -iate (parliate, prendiate). The loro form is simply the singular with -no stuck on: parli -> parlino, venga -> vengano, vada -> vadano.

The five true exceptions

Step 1 fails for exactly five verbs, and they happen to be the most common ones. Learn them as raw vocabulary: essere -> sia, avere -> abbia, sapere -> sappia, dare -> dia, stare -> stia. Everything else in Italian yields to the io-form trick. dovere needs one footnote: the usual form debba comes from the older io form debbo, not from devo (which gives the rarer deva).

Spelling, as always

Verbs in -care / -gare keep the hard sound with an h: cercare -> cerchi, pagare -> paghi. Verbs in -ciare / -giare never write two i: cominciare -> cominci, mangiare -> mangi.

The Lei imperative: the form you already knew

You have been hearing the present subjunctive since your first day in Italy without knowing it. Scusi, Senta, Guardi, Aspetti, Dica are all the lui/lei subjunctive, used as a command to the person you address as Lei. Three things follow:

• -are verbs end in -i: Parli più lentamente!, Scusi!, Giri a sinistra! This is the mirror image of the informal command from step 24, where -are takes -a (Parla!).
• The negative needs nothing new. Just add non: Non giri a destra, Non si preoccupi, Non dica niente. The infinitive rule you learned for tu (Non parlare!) does not apply to Lei.
• Clitics go in front, as separate words. With tu they weld onto the end (Dammi il libro!); with Lei they stand before the verb: Mi dia il libro, Mi dica, Si accomodi, Lo prenda, Me lo dia, Non si preoccupi. Never Dia mi, never Diami.

Forms & patterns

The regular endings. Note the vowel swap and the identical first three persons:

Why the forms look “wrong” - indicative against subjunctive, 3rd person singular:

Step 1 in action - the io indicative predicts the subjunctive:

The irregulars in full. The five in bold defy Step 1 and must be memorised:

The Lei imperative is the lui/lei column, nothing more:

Examples

Common mistakes

• Penso che sia stanco. -> Penso che lui sia stanco. With io, tu and lui/lei all sharing one form, the pronoun is the only thing that says who. Dropping it is fine in the indicative, not here.
• Credo che loro vadono via. -> Credo che loro vadano via. The loro form is the singular plus -no: vada -> vadano, never the indicative vanno with a new coat of paint.
• Parla più lentamente, per favore. (to a stranger) -> Parli più lentamente, per favore. For -are verbs, -a is the friend you say tu to and -i is the polite Lei. The two are exact opposites of what your instinct expects.
• Dia mi il libro. / Diami il libro. -> Mi dia il libro. With Lei the pronoun goes before the verb, as its own word. Attaching it (dammi) is the tu rule from step 24.
• Non dire niente, signore. -> Non dica niente, signore. The “non + infinitive” negative belongs to tu only. Lei keeps the same form for positive and negative alike.

Tips

• Drop the -o, swap the vowel. Say the io present, cut the -o, add -i (-are) or -a (everything else). That single move generates venga, faccia, vada, possa, voglia, dica, esca - every irregular except five. Memorise sia, abbia, sappia, dia, stia and you have finished the irregular list for good.
• You already speak the subjunctive. Every Scusi, Senta, Guardi, Aspetti, Prego si accomodi you have said at a counter was a present subjunctive. Learn those five as fixed vocabulary, and the mood arrives with a friendly face instead of a grammar table.
• The pronoun is part of the form. Do not think “che tu parli = parli plus an optional tu”. Think of che tu parli as one unit. Learners who train the pronoun in from day one never produce the ambiguous half-sentences that force a listener to ask chi?
• Only four forms exist per verb. Under all the noise, a subjunctive has one singular form, -iamo, -iate, and the singular + -no. Get parli / parliamo / parliate / parlino into your mouth and you own the pattern.