Learn Hardcore French: Si tu vois Marie au port, dis-lui bonjour de ma part. - If you see Marie at the harbor, say hello to her from me.

In French, after si meaning if, you don’t use the future tense. You normally use the present indicative, even when you’re talking about the future.

Typical pattern:

Si + present, then future / present / imperative in the main clause.

Examples:

Si tu vois Marie, dis-lui bonjour.
Si tu vois Marie, tu lui diras bonjour.
Si tu vois Marie, tu lui dis bonjour.

So si tu verras is incorrect in standard French. The correct form is si tu vois.

Does si ever take the subjunctive? Should it be si tu voies?

No. After si meaning if, French uses the indicative, not the subjunctive.

Correct: Si tu vois Marie… (indicative: tu vois)
Incorrect: Si tu voies Marie… (subjunctive: tu voies)

The subjunctive appears after certain conjunctions like bien que, pour que, afin que, etc., but si is not one of them when it means if.

(There is a very rare literary use of si with the subjunctive, but that’s advanced/archaic and not relevant here.)

Why is it dis-lui and not dis à elle?

French normally uses object pronouns instead of full à + person phrases when they are short and unstressed.

dire quelque chose à quelqu’un → to say something to someone
- Je dis bonjour à Marie. → Je lui dis bonjour.
- Dis bonjour à Marie. → Dis-lui bonjour.

So:

dis à elle bonjour is grammatically possible but sounds clumsy and very emphatic.
The natural form is dis-lui bonjour.

Lui is the standard indirect object pronoun for to him / to her.

Why do we use lui for Marie (a woman) and not elle?

French distinguishes between:

Indirect object pronouns (used with verbs like dire à, parler à, téléphoner à):
- lui = to him / to her
- leur = to them
Stressed (disjunctive) pronouns:
- lui = him
- elle = her (as a stressed pronoun)

In dis-lui bonjour, lui is an indirect object pronoun for à Marie:

dire bonjour à Marie → dire bonjour à elle (theoretically) → lui dire bonjour → dis-lui bonjour

You would use elle in cases like:

C’est elle. – It’s her.
Je parle d’elle. – I’m talking about her.

But after dire à quelqu’un, the correct clitic pronoun is lui, regardless of gender: lui for both him and her.

Why is there a hyphen in dis-lui?

In the imperative (command form) with object pronouns, French attaches the pronouns to the verb with a hyphen and changes the usual pronoun order.

Normal order (non-imperative):

Je lui dis bonjour. (subject + pronoun + verb)

Imperative:

Dis-lui bonjour. (verb + hyphen + pronoun)

Some patterns:

Donne-moi ça. – Give me that.
Montre-le-nous. – Show it to us.
Parlez-lui. – Speak to him / her.

So dis-lui is the imperative dis + pronoun lui with a hyphen, following the standard rule for commands.

Why is it au port and not à le port?

À le always contracts to au in French:

à + le = au
à + les = aux

So:

à le port → au port
à le cinéma → au cinéma
à les États-Unis → aux États-Unis

You only say à la (feminine singular) and à l’ (before a vowel sound):

à la plage – to the beach
à l’école – to school

Since port is masculine singular (le port), you must say au port.

What exactly does au port mean? Is it specifically a seaport?

Le port is a general word for port / harbor / dock.
Au port simply means at the port / at the harbor.

Context will tell you what kind of port:

Seaport (for ships)
River port
Sometimes, contextually, a ferry terminal, etc.

If you wanted to be more specific, you might say:

au port de plaisance – at the marina
au port maritime – at the seaport

But in everyday speech, au port is often enough.

Why do we say dis-lui bonjour de ma part instead of dis-lui bonjour de moi or pour moi?

De ma part is a fixed, idiomatic phrase meaning on my behalf / from me in greetings:

Dis-lui bonjour de ma part. – Say hello to her for me.
Passe le bonjour à Marie de ma part. – Give my regards to Marie.

You could also hear:

Dis-lui bonjour pour moi.

This is understandable and often used in casual speech. However:

de ma part sounds a bit more standard and idiomatic, especially in neutral/formal contexts.
de moi here is not idiomatic for this meaning; it sounds non-native.

So the natural choices are de ma part (very standard) or pour moi (colloquial, but fine).

Could we also say Dis bonjour à Marie de ma part? Is there a difference from dis-lui bonjour de ma part?

Yes, you can say both:

Dis-lui bonjour de ma part.
Dis bonjour à Marie de ma part.

They mean essentially the same thing. Differences:

Dis-lui bonjour uses the pronoun lui (to her).
Dis bonjour à Marie repeats the full name instead of the pronoun.

Stylistically:

Using lui avoids repeating Marie if she was already mentioned.
Using à Marie can be clearer if the listener might not remember who lui refers to.

Both are perfectly natural.

Why is the verb dis and not dises or something else? What form is dis?

Dis here is the imperative singular (command form) of dire:

Infinitive: dire – to say, to tell
Present indicative: tu dis – you say
Imperative (tu): dis – say / tell

Imperative forms of dire:

(tu) dis – say / tell (informal)
(nous) disons – let’s say / let’s tell
(vous) dites – say / tell (formal/plural)

So Dis-lui bonjour literally means Say hello to her or Tell her hello.

Can we use vous instead of tu here? How would the sentence change?

Yes, if you’re being formal or talking to more than one person, you use vous.

Informal (to one person):

Si tu vois Marie au port, dis-lui bonjour de ma part.

Formal or plural:

Si vous voyez Marie au port, dites-lui bonjour de ma part.

Changes:

tu vois → vous voyez (present of voir)
dis-lui → dites-lui (imperative of dire for vous)

Could we say Quand tu verras Marie au port, dis-lui bonjour de ma part instead of Si tu vois Marie…? What’s the difference?

Both are grammatically correct, but they express slightly different ideas:

Si tu vois Marie… – If you see Marie (you might see her, you might not). The meeting is uncertain or hypothetical.
Quand tu verras Marie… – When you see Marie (the speaker assumes you will definitely see her at some point).

So:

Si emphasizes the condition (in case you see her).
Quand emphasizes the time (at the moment when you see her).

Use si when you’re not sure the meeting will happen; quand when you’re assuming it will.