Learn Hardcore German: Am Montag arbeite ich im Büro.

Because Montag is masculine (der Montag), and an with time expressions uses the dative case, you get an dem Montag, which is always contracted to am Montag in normal speech and writing.

Just saying Montag arbeite ich im Büro is possible, but it sounds more like a heading, note, or very informal style (e.g. in a planner). The full, normal sentence would use am.

What is the difference between am Montag and montags?

They look similar but mean different things:

am Montag
→ on Monday (this particular Monday / one specific Monday)
Example:
Am Montag arbeite ich im Büro.
= On Monday (i.e. this coming / that Monday), I work in the office.
montags (lowercase, adverb)
→ on Mondays / every Monday / usually on Mondays
Example:
Montags arbeite ich im Büro.
= I work in the office on Mondays (as a regular habit).

So:

am Montag → a specific Monday
montags → habitual / repeated Mondays

Why does the sentence start with Am Montag and not with Ich?

German main clauses follow the verb‑second rule:

Exactly one element goes in first position (it can be the subject, a time expression, a place expression, etc.).
The finite verb (here: arbeite) must be in second position.
The rest of the elements follow after that.

Both are correct:

Am Montag arbeite ich im Büro.
(Time → Verb → Subject → Place)
Ich arbeite am Montag im Büro.
(Subject → Verb → Time → Place)

The word order is chosen for emphasis or flow, not for basic grammatical correctness:

Am Montag arbeite ich im Büro.
Emphasizes “on Monday” (contrast with other days).
Ich arbeite am Montag im Büro.
Neutral emphasis on the subject (“I”).

In both cases, arbeite must be second.

Could I say Am Montag ich arbeite im Büro?

No. That breaks the verb‑second rule.

With Am Montag first, the second element must be the finite verb:

✅ Am Montag arbeite ich im Büro.
❌ Am Montag ich arbeite im Büro.

In German, a normal statement can never start with “[something] + subject + verb” the way English sometimes does. The verb must be the second element.

Why is it arbeite and not arbeiten or something else?

Arbeiten is the infinitive (“to work”).
German conjugates verbs according to the subject. For arbeiten in the present tense:

ich arbeite – I work
du arbeitest – you work (singular, informal)
er/sie/es arbeitet – he/she/it works
wir arbeiten – we work
ihr arbeitet – you (plural, informal) work
sie arbeiten – they work / you (formal) work

The subject in the sentence is ich (“I”), so you need:

ich arbeite

Hence: Am Montag arbeite ich im Büro.

What does im mean, and how is it formed?

im is a contraction of in dem:

in = in
dem = dative form of “the” for masculine/neuter nouns

So:

in dem Büro → im Büro

Why dative? The preposition in can take dative (for location, “where?”) or accusative (for movement, “where to?”):

Wo? (Where?) → dative:
Ich arbeite im Büro. (Where do I work? In the office.)
Wohin? (Where to?) → accusative:
Ich gehe ins Büro. → in das Büro (into the office)

In the original sentence, im Büro describes a static location, so in + dem → im (dative).

Why is it im Büro and not auf dem Büro or some other preposition?

Different languages use different prepositions with “office”:

English: “at the office”
German: im Büro (literally “in the office”)

You would not say:

❌ auf dem Büro arbeiten (that would suggest “on top of the office building”)

Common patterns in German are:

im Büro arbeiten – to work in (at) the office
ins Büro gehen – to go to the office
vom Büro aus – from (out of) the office (as in from that location)

So im Büro is simply the idiomatic, standard expression for “at the office.”

What cases are Montag and Büro in here, and why?

Montag:
Comes after the preposition an (in the contracted form am = an dem).
an with time expressions (like days) takes the dative case.
So Montag is in the dative singular: an dem Montag → am Montag.
Büro:
Comes after in (contracted in im = in dem).
Here in expresses a location (where?), so it also takes the dative case.
Büro is neuter (das Büro), so dative singular is dem Büro → im Büro.

In both phrases, the article (dem) is hidden inside the contraction (am, im), but grammatically they’re both dative.

Why are Montag and Büro capitalized?

In German, all nouns are capitalized, regardless of their position in the sentence.

Montag is a day of the week, which is a noun → capitalized.
Büro (“office”) is also a noun → capitalized.

This is different from English, where:

“Monday” is capitalized (proper noun),
but “office” is not, unless it’s part of a name (e.g. “the Foreign Office”).

So: Am Montag arbeite ich im Büro.
Both Montag and Büro must be capitalized.

How do you pronounce Montag and Büro?

Approximate pronunciation (Standard German):

Montag: [ˈmoːnˌtaːk]
- Mon: like English “mohn”, but with a long “o”, similar to “moan” but shorter.
- tag: like “tahk” (long a as in “father”), final g is usually like a soft “k” sound: tahk.
Büro: [byˈʁoː]
- ü: this is not in English; shape your lips as if to say “oo”, but say “ee” with that lip shape.
  It’s similar to the French u in “tu”.
- r: often a soft, uvular sound in the back of the throat in Standard German.
- o at the end: a long “oh” sound.

So roughly:

Montag ≈ “MOHN-tahk”
Büro ≈ “byur-OH” (with that special ü sound)

Can I drop am and just say Montag arbeite ich im Büro in a full sentence?

You can, but it sounds marked and is not the neutral standard.

Am Montag arbeite ich im Büro. → neutral, standard.
Montag arbeite ich im Büro. → possible in spoken or very informal contexts, often sounds like a shorthand, or like contrasting with other days (“Tuesday I’m at home, Monday I’m at the office”).

In normal, careful German, especially in writing or for learners, you should keep the preposition:

Am Montag arbeite ich im Büro.