The construction como si — as if, as though — is the workhorse of hypothetical comparison in Spanish. It lets you say that someone behaves, looks, sounds or speaks in a manner that resembles a situation that isn't actually true. Habla como si lo supiera todo (he talks as if he knew everything — but he doesn't). Me miraba como si no me hubiera reconocido (she looked at me as if she hadn't recognised me — but she had). Conduce como si fuera el dueño de la carretera (he drives like he owns the road — but he doesn't).
This page focuses on como si as a sentence construction: how it shapes the broader sentence, what it does in peninsular discourse, the aspectual distinction between its two forms, and where learners go wrong. For the verb-form mechanics — the conjugation paradigms of the imperfect and pluperfect subjunctive — see verbs / subjunctive imperfect / como si.
The non-negotiable rule
After como si, the verb is always in the imperfect subjunctive or the pluperfect subjunctive. There is no exception. Not the indicative. Not the present subjunctive. Not the simple past. Modern Spanish allows exactly two options.
Habla como si supiera todo.
He talks as if he knew everything.
Me trata como si fuera idiota.
He treats me as if I were an idiot.
Lo cuenta como si hubiera estado allí.
He tells it as if he'd been there.
The reason is built into the meaning: como si asserts a comparison with something that is by definition not the case. Counterfactuality is the semantic core of the construction, and Spanish marks counterfactuality with the subjunctive. The indicative would imply the comparison is real — which would make como si nonsense.
The aspectual choice: imperfect vs pluperfect
You have one decision to make after picking como si: which subjunctive — imperfect or pluperfect? The answer turns on a single question.
Does the hypothetical situation occur at the same time as the main clause, or before it?
- Same time (simultaneous) → imperfect subjunctive (
fuera,tuviera,supiera,estuviera,hubiera). - Earlier than the main clause (prior, anterior) → pluperfect subjunctive (
hubiera + participle).
| Time relation | Form | Example |
|---|---|---|
| Simultaneous with main clause | Imperfect subj. | Habla como si supiera todo. |
| Prior to main clause | Pluperfect subj. | Habla como si lo hubiera visto con sus propios ojos. |
Simultaneous: imperfect subjunctive
The hypothetical state holds at the moment of the comparison. He talks (now) as if he knew (now).
Anda como si tuviera miedo de algo.
He walks as if he were afraid of something.
Conduce como si fuera el dueño de la carretera.
He drives like he owns the road.
Me sonrió como si nos conociéramos de toda la vida.
She smiled at me as if we'd known each other forever.
Mi vecino vive como si el dinero no fuera un problema.
My neighbour lives like money is no problem.
In every case, the hypothetical state (tener miedo, ser el dueño, conocerse, no ser un problema) is simultaneous with the matrix verb (anda, conduce, me sonrió, vive). Even when the matrix is in the past (me sonrió), the imperfect subjunctive still marks simultaneity — we knew each other at that same moment of smiling.
Prior: pluperfect subjunctive
The hypothetical event happened before the moment of the comparison. He looked at me (then) as if he hadn't recognised me (already, beforehand).
Me miraba como si no me hubiera reconocido.
He looked at me as if he hadn't recognised me.
Reaccionó como si lo hubiera ofendido gravemente.
He reacted as if I'd seriously offended him.
Habla del partido como si lo hubiera jugado él mismo.
He talks about the match like he'd played in it himself.
Llegó a la oficina como si no hubiera dormido en tres días.
He turned up at the office as if he hadn't slept for three days.
In each case, the hypothetical event (reconocerme, ofenderlo, jugarlo, dormir) precedes the matrix verb. The pluperfect captures that before relation.
The aspect choice is the same logic that governs the difference between I knew and I had known in English narrative. Anchor the matrix verb in its time; then ask whether the hypothetical is happening at that time (imperfect) or has already happened by that time (pluperfect).
Negative como si
Negation sits inside the como si clause as usual, and the subjunctive mood is unaffected.
No me trates como si fuera tonto.
Don't treat me like I'm stupid.
Habla del tema como si no le importara nada.
He talks about the subject as if he didn't care at all.
Pasaron por delante como si no me hubieran visto.
They walked past as if they hadn't seen me.
Variants and synonyms
Several constructions cover similar territory; each takes the same subjunctive forms.
| Variant | Register | Example |
|---|---|---|
| como si | neutral (everyday + written) | Habla como si lo supiera todo. |
| igual que si | colloquial (peninsular) | Habla igual que si lo supiera todo. |
| lo mismo que si | colloquial | Es lo mismo que si no hubieras dicho nada. |
| cual si | literary, archaic | Permaneció en silencio, cual si nada hubiera pasado. |
| ni que | colloquial, ironic | ¡Ni que fueras mi madre! |
The last one — ni que — is a peninsular conversational gem worth knowing. It expresses indignant rejection of an implied comparison: ¡Ni que fueras mi madre! literally "not even if you were my mother", idiomatically "you're not my mother, stop acting like it." It always takes the imperfect subjunctive, follows the same rule as como si, and is firmly informal.
—Tienes que recoger tu cuarto. —¡Ni que fueras mi madre!
—You have to tidy your room. —You're not my mother! (lit. 'not even if you were my mother')
¡Como si...! as a standalone exclamation
A second peninsular conversational gem: como si can stand alone (with no main clause at all) as an ironic dismissal — meaning "as if!" or "yeah right, like that's going to happen / like I didn't know already." This usage is firmly informal and very common in spoken Spanish.
—Te lo digo en serio, esta vez sí que llego a tiempo. —¡Como si no te conociera!
—I'm serious, this time I'll be on time. —As if I didn't know you!
—Es que no sabía que estaba prohibido. —¡Como si no lo supieras!
—I didn't know it was forbidden. —As if you didn't know!
¡Como si yo no tuviera otras cosas que hacer!
As if I didn't have other things to do!
The exclamatory ¡como si...! always sits in the imperfect subjunctive (occasionally pluperfect), is heavily sarcastic, and functions almost like a back-channel response. Recognise it; native speakers use it daily.
Como si is not a conditional
Despite living near the conditionals on the grammar map, como si is not a conditional construction — it's a comparative one. It doesn't introduce a hypothesis whose consequence the main clause spells out; it introduces a comparison-point that the main clause is being measured against.
- Si supiera todo, lo diría — conditional. "If he knew everything, he'd say so." The hypothesis knowing everything triggers a hypothetical result saying so.
- Habla como si lo supiera todo — comparative. "He talks as if he knew everything." His actual talking is being compared to the talking of a hypothetical know-it-all.
The structural consequence: como si never licenses a conditional or conditional-perfect main clause. The main verb of a como si sentence is in whatever tense the description requires (often present, imperfect, or preterite), never -ría or habría + part.
❌ Habla como si lo supiera todo, lo diría todo.
Wrong on two counts: the second clause looks like a conditional result, but como si is not a conditional, and the conditional 'diría' has nothing to attach to.
✅ Habla como si lo supiera todo.
He talks as if he knew everything. (no further clause needed)
For the proper conditional patterns, see mixed conditionals.
Position in the sentence
Como si clauses follow the matrix verb as adverbial modifiers. They almost never front the sentence, unlike si-clauses, which freely sit at the start.
Me miró como si no me conociera.
He looked at me as if he didn't know me. (natural)
Como si no me conociera, me miró.
As if he didn't know me, he looked at me. (heavy, literary; rarely used in conversation)
Inverting works only in narrative or literary style and creates a contrastive emphasis on the comparison itself. In everyday speech, keep the como si clause where it naturally falls — after the matrix verb.
Common Mistakes
❌ Habla como si sabe todo.
Wrong — como si never takes the indicative. The mood must be subjunctive.
✅ Habla como si lo supiera todo.
He talks as if he knew everything.
❌ Habla como si sepa todo.
Wrong — present subjunctive (sepa) is not allowed after como si. Only imperfect or pluperfect subjunctive.
✅ Habla como si supiera todo.
He talks as if he knew everything.
❌ Me miraba como si no me reconociera.
Aspect mismatch — the failure to recognise happened before the looking, so the pluperfect is required, not the imperfect.
✅ Me miraba como si no me hubiera reconocido.
He was looking at me as if he hadn't recognised me.
❌ Habla como que lo sabe todo.
Wrong — the conjunction is 'si', not 'que'. ('Como que' exists but with a different meaning: roughly 'it's as if' as a hedge.)
✅ Habla como si lo supiera todo.
He talks as if he knew everything.
❌ Lo cuenta como si habría estado allí.
Wrong — the conditional (habría) is not allowed after como si. Use the pluperfect subjunctive.
✅ Lo cuenta como si hubiera estado allí.
He tells it as if he'd been there.
Key takeaways
- Como si always takes the imperfect or pluperfect subjunctive — never the indicative, never the present subjunctive, never the conditional.
- Aspect choice: imperfect subjunctive for simultaneous with the main clause; pluperfect subjunctive for prior to it.
- Como si is a comparative construction, not a conditional one. It doesn't license a -ría or habría main clause.
- Recognise the peninsular conversational uses: ¡como si...! as ironic dismissal, ni que... as indignant rejection.
- Variants — igual que si, lo mismo que si, cual si — follow the same mood rule.
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- Condicionales mixtosB2 — Mixed conditionals combine a past hypothetical with a present consequence, or a present trait with a past outcome — built by matching each clause's tense to the time it lives in, not by fixed pairings.
- De + infinitivo: condicional alternativoB2 — A formal alternative to si-clauses: 'de + infinitive' compresses the conditional protasis into a non-finite phrase — concise, written-register, and beloved of journalism and oratory.
- Como si + imperfecto de subjuntivoB1 — Como si ('as if') always demands the imperfect or pluperfect subjunctive in modern Spanish — never the indicative, never the present subjunctive.
- Imperfecto de subjuntivo en -raB2 — Build the -ra forms of the imperfect subjunctive from the preterite stem and use them in past triggers, counterfactual si-clauses, and ojalá-wishes.
- Usos del pluscuamperfecto de subjuntivoB2 — The pluperfect subjunctive (hubiera/hubiese hablado) is Spanish's tense of regret, counterfactual past, and back-shifted prior events — used in si-clauses, ojalá-wishes, and after past triggers.
- Comparaciones hipotéticas: 'como si fuera'B1 — Hypothetical comparisons in Spanish — como si and ni que with imperfect or pluperfect subjunctive — used to liken a real event to an unreal one for irony, exaggeration, or vivid description.