Learn Hardcore German: Der Kollege kann heute nicht zusagen, aber seine Teilnahme ist sonst sicher. - The male colleague cannot commit today, but otherwise his participation is certain.

Here zusagen means to accept or confirm participation (roughly “to RSVP/commit”). It does not mean “to say” here, and it’s not the other sense of zusagen meaning “to appeal to/please” (as in Das Essen sagt mir zu = “I like the food”).

Examples:

Er sagt zu. = He accepts/commits.
Er hat zugesagt. = He confirmed/said yes.
Contrast: Die Farbe sagt mir zu. = I find the color appealing.

Why is zusagen at the end in kann heute nicht zusagen?

Zusagen is a separable-prefix verb (zu- + sagen). In a simple present main clause without a modal it separates: Er sagt heute nicht zu. With a modal verb like können, the main verb stays as an infinitive at the end and the prefix reattaches: Er kann heute nicht zusagen.

Key forms:

Present, no modal: er sagt zu
With modal: er kann zusagen
Perfect: er hat zugesagt
Simple past: er sagte zu

Why heute nicht, not nicht heute? Is there a difference?

Default placement is heute nicht (“not today”), with nicht following the time adverb. Nicht heute is also possible but puts contrastive focus on “today” (implying “not today, but some other day”). So:

Er kann heute nicht zusagen. = He can’t confirm today (a neutral statement).
Er kann nicht heute zusagen, sondern morgen. = Specifically not today, but tomorrow.

What does sonst mean here?

Sonst here means “otherwise / in other respects / under other circumstances.” So seine Teilnahme ist sonst sicher = apart from today’s issue, his participation is certain. Note that sonst can also mean “or else” in warnings (e.g., Beeil dich, sonst verpasst du den Zug), but not in this sentence.

Why is it Der Kollege and not Ein Kollege or Mein Kollege?

The definite article der points to a specific colleague identifiable from context (someone both speaker and listener can figure out). Alternatives:

Ein Kollege = some colleague (introduces a new, unspecified person)
Mein Kollege/unser Kollege = explicitly marks possession/affiliation

How does seine Teilnahme work? Does seine agree with the possessor or the noun?

Possessives in German reflect both the possessor (root sein- = “his/its” for a male/neutral possessor) and the gender/number/case of the possessed noun in their ending.

Possessor: the colleague (male), so use sein-.
Possessed noun: Teilnahme is feminine and is the subject (nominative singular), so add -e: seine Teilnahme.

If the possessor were female (e.g., die Kollegin), you’d use ihre Teilnahme.

What is the gender and typical use of Teilnahme?

Gender: feminine (die Teilnahme).
Meaning: attendance/participation.
Typical collocation: Teilnahme an + Dativ (participation in something), e.g., seine Teilnahme an der Sitzung.
It’s derived from the verb teilnehmen (to participate): Er nimmt teil / Er hat teilgenommen.

The tense is present. Is it talking about the future?

Yes. German often uses the present to talk about future arrangements when there’s a time expression: Der Kollege kann heute nicht zusagen (today). Likewise ist sicher can express future certainty about the event. A future auxiliary (wird) is not required here.

Why is there a comma before aber, and what does it do to word order?

Aber is a coordinating conjunction. In German you place a comma before coordinating conjunctions that join two independent clauses. Both clauses keep normal main-clause verb-second order:

Der Kollege kann …, aber seine Teilnahme ist …

Could we use absagen instead of nicht zusagen?

No. Absagen means to decline or cancel (to say no). Nicht zusagen here means “can’t commit/confirm (yet).” They’re different:

Er sagt ab. = He declines/cancels.
Er sagt (heute) nicht zu. = He doesn’t/can’t accept today.
A near-synonym of zusagen is bestätigen (to confirm), though zusagen is the standard for accepting an invitation.

Is the sentence formal or informal?

Neutral-professional. Words like Kollege, Teilnahme, zusagen are common in workplace or organizational contexts and fit both spoken and written communication.

Can I front the time expression?

Yes. Heute kann der Kollege nicht zusagen, aber seine Teilnahme ist sonst sicher. This is very natural and keeps the same meaning. In German, moving adverbials like heute to the first position is common.

Can I move sonst earlier: … aber sonst ist seine Teilnahme sicher?

Yes. Both are fine:

… aber seine Teilnahme ist sonst sicher. (slight focus on the participation)
… aber sonst ist seine Teilnahme sicher. (slight focus on the contrastive adverb “otherwise”) The meaning is effectively the same.

Are there synonyms for sicher here?

Yes, depending on tone:

Neutral: sicher, gewiss
More idiomatic/colloquial: steht fest (e.g., seine Teilnahme steht fest)
Stronger commitment: fest zugesagt (e.g., Er hat sonst fest zugesagt) Be careful: vermutlich means “probably,” which is weaker than sicher.

Does kann … nicht express inability, lack of permission, or something else?

With zusagen, it usually means “not in a position to commit now” (could be due to missing information, scheduling uncertainty, or constraints). It’s not about physical ability. Context decides whether it’s inability, lack of opportunity, or not being authorized to confirm yet.

How does Kollege decline? I’ve seen forms with -n.

Kollege is a weak (n-declension) masculine noun. Singular adds -n/-en in every case except nominative:

Nominative: der Kollege
Accusative: den Kollegen
Dative: dem Kollegen
Genitive: des Kollegen Plural: die Kollegen (and then -n in dative plural: den Kollegen).

Is zusagen the same as zu sagen?

No. Zusagen (one word) is a separable-prefix verb meaning “to accept/confirm” or “to appeal.” Zu sagen (two words) is an infinitive with zu + sagen (“to say”), as in nichts zu sagen (“nothing to say”). They’re different verbs/structures.

Can I use a noun instead of the verb: keine Zusage?

Yes. Common alternatives:

Der Kollege kann heute keine Zusage machen/geben, aber seine Teilnahme ist sonst sicher.
Es gibt heute noch keine Zusage von dem Kollegen, … These are slightly more formal or bureaucratic but perfectly idiomatic.