Como si translates as as if, as though, like — and it is one of the few constructions in Spanish that gives you zero choice of mood. It always takes the imperfect subjunctive, or the pluperfect subjunctive when the comparison reaches into the past. The present indicative, the present subjunctive, the simple past — none of them work here. This is one of the cleanest, most rule-bound corners of Spanish grammar, which makes it a great early win for B1 learners.
The core rule
After como si, the verb is always in the imperfect subjunctive (for a hypothetical state simultaneous with the main clause) or in the pluperfect subjunctive (for a hypothetical state prior to the main clause).
Habla como si supiera todo.
He talks as if he knew everything.
Me trata como si fuera tonta.
He treats me as if I were stupid.
Lo cuenta como si hubiera estado allí.
He tells it as if he had been there.
The reason is logic, not arbitrariness. Whatever follows como si is by definition not the case — it is a comparison with a hypothetical, counterfactual situation. He talks as if he knew everything implies he does not actually know everything. Spanish marks that counterfactuality grammatically by using the subjunctive; the indicative would imply the comparison is real, which contradicts the meaning of como si itself.
Imperfect subjunctive vs pluperfect subjunctive
Both are available. The choice depends on the time relationship between the hypothetical and the main clause.
- Use the imperfect subjunctive when the hypothetical state is simultaneous with the main action (he acts now as if he knew now).
- Use the pluperfect subjunctive when the hypothetical state is prior to the main action (he acts now as if he had known earlier, or as if something had happened before).
Me mira como si me conociera de toda la vida.
She looks at me as if she had known me her whole life (and still does).
Me miró como si me hubiera conocido en otra vida.
She looked at me as if she had known me in another life.
In the first sentence, the (imagined) knowing is simultaneous with the looking. In the second, the (imagined) knowing took place before the looking, so the pluperfect subjunctive is required.
Both -ra and -se work in Spain
As with every imperfect subjunctive in peninsular Spanish, you can freely choose -ra or -se forms. They are interchangeable; some speakers gravitate toward one or the other without consistency.
Actúa como si fuese el dueño del bar.
He acts like he owned the bar.
Actúa como si fuera el dueño del bar.
He acts like he owned the bar.
The same applies to the pluperfect subjunctive — hubiera and hubiese are both fine:
Lo dice como si lo hubiese vivido en carne propia.
He says it as if he had lived it himself.
Lo dice como si lo hubiera vivido en carne propia.
He says it as if he had lived it himself.
In real conversations
These are the kinds of sentences peninsular speakers actually produce on the street, in the office, and at the dinner table. Notice how natural the construction feels: it is not bookish, it is everyday.
Mi jefe me habla como si no tuviera ni idea de mi trabajo.
My boss talks to me as if I had no idea about my job.
Pones esa cara como si te hubiera ofendido algo que dije.
You're making that face as if something I said had offended you.
Estaba tan callado que parecía como si no le interesase la conversación.
He was so quiet that it seemed as if the conversation didn't interest him.
Después de tantos años fuera, vuelvo al pueblo y es como si nunca me hubiera ido.
After so many years away, I come back to the village and it's as if I had never left.
The final example is a classic — como si nunca me hubiera ido is so common in nostalgic talk about returning home that it almost qualifies as a fixed phrase.
The vosotros forms
Peninsular Spanish needs the vosotros imperfect and pluperfect subjunctive whenever you address a group informally. The endings are -rais / -seis (no accent) for the imperfect and hubierais / hubieseis for the pluperfect.
Estáis aquí como si fuerais los reyes del lugar.
You guys are here as if you were the kings of the place.
Lo contáis como si hubierais visto la escena con vuestros propios ojos.
You tell it as if you had seen the scene with your own eyes.
Watch the accent on fuerais and hubierais: there isn't one. Learners often want to add one by analogy with habláis, but the imperfect subjunctive vosotros forms are unaccented.
Why not the present subjunctive?
Many learners, especially those who have just learned the present subjunctive after triggers like quiero que and espero que, want to extend that pattern to como si. Their instinct is to write como si sepa or como si tenga. This is always wrong in modern Spanish.
❌ Habla como si sepa todo.
Incorrect — como si never takes the present subjunctive.
✅ Habla como si supiera todo.
He talks as if he knew everything.
The reason: como si by its meaning sets up a hypothetical comparison, which requires the imperfect subjunctive (the mood-and-tense of present counterfactuals), exactly the same form you'd use after si in a type-2 conditional. The present subjunctive is the mood of triggered clauses (after verbs of wish, doubt, emotion), which is a completely different mechanism. Como si is more like si tuviera than like quiero que tenga.
Why not the indicative?
The other common error is using the indicative because como si feels descriptive — you are describing what someone is doing.
❌ Habla como si sabe todo.
Incorrect — como si never takes the indicative.
✅ Habla como si supiera todo.
He talks as if he knew everything.
There is exactly one variant where the indicative can appear: como without si (just como) followed by an indicative clause means the way that or just like, and it is not the same construction at all. Habla como yo hablo means he talks the way I talk (a real comparison). Habla como si supiera todo means he talks as if he knew everything (a hypothetical comparison). Different word, different mood.
"Ni que" — an emphatic cousin
You may hear or read ni que in spoken peninsular Spanish, especially in exasperated reactions. It functions like an emphatic como si with implied disbelief.
¡Ni que fuera el primer día de clase! (informal)
As if it were the first day of school! (You're acting like a total beginner.)
¡Ni que tuviéramos todo el día! (informal)
As if we had all day! (Hurry up.)
The mood rule is the same: ni que takes the imperfect or pluperfect subjunctive, never the indicative. It's just como si with extra attitude.
Common Mistakes
❌ Me habla como si me conoce.
Incorrect — indicative is never used after como si.
✅ Me habla como si me conociera.
He talks to me as if he knew me.
❌ Actúa como si sea el jefe.
Incorrect — the present subjunctive does not appear after como si.
✅ Actúa como si fuera el jefe.
He acts as if he were the boss.
❌ Lo cuenta como si estaba allí.
Incorrect — the imperfect indicative does not work here; you need the pluperfect subjunctive for a prior state.
✅ Lo cuenta como si hubiera estado allí.
He tells it as if he had been there.
❌ Me trata como si soy un niño.
Incorrect — present indicative cannot appear after como si.
✅ Me trata como si fuera un niño.
He treats me as if I were a child.
❌ Hablas como si todo es fácil.
Incorrect — indicative is impossible here.
✅ Hablas como si todo fuera fácil.
You talk as if everything were easy.
The single cure for all five is the same: after como si, your verb must be in the imperfect subjunctive (for simultaneous time) or the pluperfect subjunctive (for prior time). There are no exceptions in modern standard Spanish.
Key takeaways
- Como si always takes the imperfect or pluperfect subjunctive — never the indicative, never the present subjunctive.
- Use the imperfect subjunctive when the hypothetical is simultaneous with the main clause; the pluperfect subjunctive when it is prior.
- Both -ra and -se forms are fully acceptable in Spain.
- The vosotros forms (fuerais, hubierais) carry no accent.
- Ni que is an emphatic colloquial variant that follows the same mood rules.
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