Como Si | Spanish (Latin America) Grammar

The expression como si ("as if") is one of the most reliable triggers for the imperfect subjunctive in Spanish. It introduces a comparison with something that is not true — a pretense, an appearance, or a hypothetical behavior. Unlike most subjunctive triggers, como si does not care about the tense of the main clause: it always takes the imperfect subjunctive, even when the main clause is in the present.

The Basic Rule

Como si + imperfect subjunctive. Always. No exceptions.

Habla como si supiera todo.

He talks as if he knew everything.

Notice something unusual: the main verb habla is in the present, but the dependent verb supiera is in the imperfect subjunctive. This would normally break the sequence of tenses, but como si is special. It signals an unreal comparison, and unreal comparisons about the present are always expressed with the imperfect subjunctive.

Why the Imperfect Subjunctive?

The logic is the same as in Type 2 si-clauses. "As if" introduces a contrary-to-fact situation: he does not in fact know everything, but he acts that way. Spanish marks this gap between appearance and reality with the imperfect subjunctive, regardless of when the observation is made.

Se comporta como si fuera un niño.

He behaves as if he were a child.

Me mira como si no me conociera.

She looks at me as if she didn't know me.

Common Patterns

Main Clause Tense	Como Si Clause	Example
Present	Imperfect subjunctive	Habla como si supiera.
Preterite	Imperfect subjunctive	Habló como si supiera.
Imperfect	Imperfect subjunctive	Hablaba como si supiera.
Conditional	Imperfect subjunctive	Hablaría como si supiera.
Future	Imperfect subjunctive	Hablará como si supiera.

The imperfect subjunctive stays put regardless of what happens in the main clause.

Never Use Present Subjunctive

A natural mistake for English speakers is to try the present subjunctive: "Habla como si sepa todo." This is wrong. Spanish does not allow the present subjunctive after como si, ever.

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Remember: como si + imperfect subjunctive is a fixed collocation. Think of it almost as a single unit: como-si-supiera, como-si-fuera.

Common Examples

Gasta dinero como si fuera millonario.

He spends money as if he were a millionaire.

La casa está en silencio, como si no viviera nadie.

The house is silent, as if no one lived there.

Me trata como si yo fuera su hermana menor.

She treats me as if I were her little sister.

With Ser and Estar

Como si fuera and como si estuviera are particularly common set phrases:

Está pálido, como si estuviera enfermo.

He is pale, as if he were sick.

Habla español como si fuera nativo.

He speaks Spanish as if he were a native.

Idiomatic Uses

Spanish also has a few idioms built on como si:

Como si nada — "as if nothing happened," "no big deal."
Como si tal cosa — "as if it were nothing," totally unfazed.
Como si lo viera — "as if I were seeing it," meaning "I can just picture it."

Le dije todo y me contestó como si nada.

I told him everything and he answered as if nothing had happened.

Past Events: Past Perfect Subjunctive

For "as if something had happened" — an earlier, completed event — you upgrade to the pluperfect subjunctive (hubiera + participle):

Llegó como si hubiera corrido un maratón.

He arrived as if he had run a marathon.

This is a natural extension of the rule: the imperfect subjunctive handles simultaneous or present-feeling unreal comparisons, the pluperfect subjunctive handles earlier ones.

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The key insight is that como si is always unreal. If the comparison were real, Spanish would just use como + indicative ("Habla como su padre" = "He talks like his father"). The subjunctive is what flags the "as if" as hypothetical.

Return to -ra forms for conjugation review, or continue to polite forms with quisiera.