Learn Hardcore German: Ich spreche morgen mit meiner Kollegin im Büro. - Tomorrow I speak with my colleague in the office.

Because mit always takes the dative case. Kollegin is feminine, and the dative feminine form of the possessive mein is meiner. So: mit meiner Kollegin = with my (female) colleague. For comparison: masculine/neuter dative would be mit meinem …, plural dative mit meinen … (and the noun usually adds -n in the dative plural if it doesn’t already end in -n).

What does im mean?

im is the contraction of in dem. You use it here because you’re talking about being located inside a place (the office), which calls for dative: in dem Büro → im Büro.

Why is it dative with in here? When would it be accusative?

German two-way prepositions (like in, auf, an) take:

Dative for location (answering “where?”): im Büro (in the office).
Accusative for direction/motion (answering “where to?”): ins Büro (into the office). Your sentence describes where the speaking will happen, not movement.

Can I start the sentence with Morgen?

Yes. German is a verb-second language, so if you front Morgen, the finite verb still stays in second position: Morgen spreche ich mit meiner Kollegin im Büro. You can also front other elements for emphasis: Im Büro spreche ich morgen mit meiner Kollegin.

Do I need future tense (e.g., Ich werde morgen sprechen), or is the present tense okay?

The present tense with a time word like morgen is the most natural choice for planned future actions: Ich spreche morgen … Use werden + infinitive for predictions, emphasis, or when timing isn’t otherwise clear.

Should it be sprechen mit, sprechen zu, reden mit, or sich unterhalten mit?

sprechen mit = have a conversation with someone (neutral, common).
reden mit = like sprechen mit, a bit more informal.
sich unterhalten mit = chat/talk with (often implies a more social conversation).
sprechen zu = speak to/address (one-way, e.g., a speech): Der Chef spricht zu den Mitarbeitenden.

How do I mention the topic of the conversation?

Use über + accusative for the topic: Ich spreche morgen mit meiner Kollegin im Büro über das Projekt. Person: mit; topic: über.

What if the colleague is male or there are several colleagues?

Male colleague (note the weak noun): mit meinem Kollegen (not “Kollege” in dative).
Several colleagues (mixed or all-male): mit meinen Kollegen.
Several female colleagues: mit meinen Kolleginnen.

Why are Kollegin and Büro capitalized, but morgen is not?

All German nouns are capitalized, so Kollegin and Büro get capitals. morgen is an adverb meaning “tomorrow,” so it’s lowercase. Capital Morgen is the noun “morning” (e.g., am Morgen = in the morning).

Could I say bei der Arbeit instead of im Büro?

You can, but it’s a bit different:

im Büro = inside the office (the room/workspace).
bei der Arbeit = at work (more general; could be anywhere you work).
auf der Arbeit is regionally common (especially in parts of Germany), but some consider bei der Arbeit more standard.

Is the order morgen mit meiner Kollegin im Büro important?

The typical neutral order follows “time–manner–place” (often taught as TeKaMoLo): morgen (time) – mit meiner Kollegin (comitative/manner) – im Büro (place). Other orders are possible for emphasis, but this one sounds most neutral.

Why isn’t there a comma after morgen?

No comma is needed when you simply start with an adverb like Morgen. Commas are used before/after clauses and certain infinitive constructions, not just after a fronted time word.

Any pronunciation tips for this sentence?

Ich: the “ch” is the soft ich-sound [ç], not like English “k”.
spreche: stress the first syllable; the final -e is a light schwa.
morgen: the “r” is uvular; the “g” is a hard [g].
Büro: rounded ü ([y]); stress on the second syllable: bü-RO.

Can I drop ich and just say Spreche morgen …?

No. German normally requires the subject pronoun; dropping it (like in Spanish or Italian) isn’t standard: Ich spreche morgen … is required.

Why is it spreche and not spricht?

It’s verb conjugation. sprechen is irregular:

ich spreche
du sprichst
er/sie/es spricht
wir sprechen
ihr sprecht
sie/Sie sprechen

Are there other common contractions like im?

Yes:

am = an dem
beim = bei dem
vom = von dem
zum = zu dem
zur = zu der
ins = in das They’re very common in everyday German.

How would I say “tomorrow morning” with this sentence?

Use morgen früh or specify the part of the day: Ich spreche morgen früh mit meiner Kollegin im Büro. You can also say morgen Vormittag (tomorrow late morning).