Learn Hardcore French: Si j’avais su, je t’aurais attendu sur le quai. - If I had known, I would have waited for you on the platform.

Si j’avais su: plus-que-parfait (imperfect of avoir/être
- past participle). It sets up an unreal condition in the past.
je t’aurais attendu: conditionnel passé (conditional of avoir/être
- past participle). It expresses the unreal past result of that condition. This is the standard “Type 3” if-clause pattern for past counterfactuals: Si + plus-que-parfait → conditionnel passé.

Why is it Si j’avais su and not Si j’aurais su?

After si (if) to express a condition, French does not use the conditional. Use present, imparfait, or plus-que-parfait in the si-clause. So:

Correct: Si j’avais su, …
Incorrect in standard French: Si j’aurais su, … (sometimes heard colloquially, but avoid it in careful speech and writing).

How are j’avais su and je t’aurais attendu formed?

j’avais su = imparfait of avoir (avais) + past participle of savoir (su).
je t’aurais attendu = conditional of avoir (aurais) + past participle of attendre (attendu). Remember: conditionnel passé is the conditional of the auxiliary + past participle.

Would Si je savais, je t’attendrais mean the same thing?

No.

Si je savais, je t’attendrais = present-time hypothetical (If I knew now, I would wait for you).
Si j’avais su, je t’aurais attendu = past-time counterfactual (Had I known then, I would have waited).

What does the t’ stand for, and why is it placed there?

t’ is the object pronoun te (you, informal). In compound tenses, object pronouns go before the auxiliary: je t’aurais attendu. It contracts to t’ before a vowel sound (here, a- in aurais).

Shouldn’t attendu agree with t’ (te)? Should it be attendue?

With avoir, the past participle agrees with a preceding direct object. Since attendre quelqu’un takes a direct object, you mark agreement:

Speaking to a male: Je t’aurais attendu.
Speaking to a female: Je t’aurais attendue.
Speaking to several people: Je vous aurais attendus/attendues (depending on gender). In everyday speech you won’t hear the difference; in careful writing, agreement is expected.

Why is it attendre quelqu’un and not attendre pour quelqu’un?

Attendre takes a direct object with no preposition: attendre quelqu’un (to wait for someone).
Use attendre pour + infinitive to mean “wait to do something” (e.g., attendre pour partir = wait before leaving), but not for people.

What’s the difference between je t’aurais attendu and je t’aurai attendu?

je t’aurais attendu = conditional perfect: “I would have waited (but didn’t).”
je t’aurai attendu = future perfect: “I will have waited (by the time you arrive).” They differ in both time reference and certainty.

Do I need the comma after the si-clause?

Yes, if the si-clause comes first: Si j’avais su, je t’aurais attendu…
No comma if the si-clause comes second: Je t’aurais attendu… si j’avais su.

Any pronunciation tips for the whole sentence?

Approximate IPA:

Si j’avais su: [si ʒavɛ sy]
je t’aurais attendu: [ʒə toʁɛ zatɑ̃dy] (note the liaison: aurais‿attendu → [z])
sur le quai: [syʁ lə kɛ]
Notes: quai is pronounced “keh” [kɛ], not like English “quay” (“kee”). The elisions in j’avais and t’aurais are mandatory.

What exactly is quai, and is sur le quai the right preposition?

un quai (masculine): a train platform or a riverside dock/embankment.
At a station, you stand sur le quai (on the platform).
With ships, à quai means “moored at the quay.”
Regionally, you may hear au quai 3 (“at platform 3”), but in France many announcements use voie 3 instead.

Could I say Si je l’avais su instead of Si j’avais su?

Yes. Si je l’avais su explicitly refers to a specific fact just mentioned (“if I had known it”). Si j’avais su can stand alone idiomatically (“Had I known…”), with the object implied by context.

How would it change with vous instead of tu?

Si j’avais su, je vous aurais attendu.
Agreement in writing depends on who “vous” is:
One woman: attendue
One man or mixed/unknown: attendu
Several women: attendues
Several men/mixed: attendus

Why does attendre use avoir and not être as the auxiliary?

Because attendre is a transitive verb. In compound tenses, most transitive verbs take avoir. Être is used with a limited set (notably many intransitive movement verbs and all pronominal verbs).

Why use savoir (su) and not connaître?

Use savoir for knowing a fact or that something is the case: Si j’avais su…
Connaître is for being familiar with someone/something: you’d say Je connais Marie/Paris, not for a fact. So Si j’avais connu here would be incorrect.