The Spanish phrase como si means "as if" or "as though." It introduces a comparison to something that isn't actually true — the speaker is describing real behavior by likening it to an imagined situation. Because the comparison is always unreal, como si has one of the strictest grammar rules in the language.
The rule
Como si always takes the subjunctive, and only in two tenses:
- Imperfect subjunctive — when the imagined comparison is at the same time as the main verb
- Pluperfect subjunctive — when the imagined comparison is earlier than the main verb
It never takes the present, never takes the future, and never takes the indicative of any tense. The rule is absolute.
Actúa como si nada hubiera pasado.
She acts as if nothing had happened.
The first sentence uses the imperfect subjunctive (supiera) because the imagined knowing is happening now, at the same time as the talking. The second uses the pluperfect subjunctive (hubiera pasado) because the imagined event is earlier than the acting.
With the imperfect subjunctive
Use the imperfect subjunctive when the unreal situation overlaps in time with the main clause. The main verb can be present, past, or future — what matters is whether the comparison is simultaneous.
Me mira como si fuera un fantasma.
He looks at me as if I were a ghost.
Corrían como si tuvieran miedo de algo.
They were running as if they were afraid of something.
In every case, the speaker knows the comparison isn't true — I'm not a ghost, we weren't really children, and they may or may not have been afraid. The imperfect subjunctive is the flag for unreality.
With the pluperfect subjunctive
When the imagined situation is earlier than the main clause, use the pluperfect subjunctive (hubiera + past participle). This is the "as if X had happened" pattern.
Me saludó como si no me hubiera visto en años.
He greeted me as if he hadn't seen me in years.
Camina como si hubiera corrido un maratón.
He walks as if he had run a marathon.
Lo dijiste como si lo hubieras ensayado mil veces.
You said it as if you had rehearsed it a thousand times.
The comparison in each case is a past event that didn't really happen. The hubiera form locks that earlier-than-now reading into place.
Never use the present
This is the single rule that trips up learners most. In English you can say "as if he knows everything" — a present-tense verb works fine. In Spanish the equivalent is always wrong:
| Wrong | Right |
|---|---|
| como si sabe todo | como si supiera todo |
| como si es mi jefe | como si fuera mi jefe |
| como si no entiende | como si no entendiera |
If you remember only one thing about como si, let it be this: the verb that follows is never in the present indicative.
A related expression
The phrase ni que is a close cousin. It introduces a rhetorical "as if!" — mocking an idea the speaker considers absurd — and it takes exactly the same subjunctive tenses.
¡Ni que fuera millonaria!
As if I were a millionaire!
Common situations
Como si shows up constantly when describing behavior, attitude, or style. You'll hear it in criticism, in storytelling, and in admiration.
Cantas como si fueras profesional.
You sing as if you were a professional.
Related Topics
- Type 2: ImprobableB2 — Pair an imperfect-subjunctive si-clause with a conditional result clause for hypothetical or unlikely present situations.
- Type 3: Contrary-to-Fact PastC1 — Use the pluperfect subjunctive with the conditional perfect to talk about past situations that didn't actually happen.
- Mixed ConditionalsC1 — Combine past and present in a single conditional to talk about how what didn't happen then still shapes how things are now.