das Argument
argument
A reason or justification put forward to support an opinion or prove a claim.
Sein stärkstes Argument war, dass das Projekt zu teuer sei.
His strongest argument was that the project was too expensive.

argument
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argument
A reason or justification put forward to support an opinion or prove a claim.
Sein stärkstes Argument war, dass das Projekt zu teuer sei.
His strongest argument was that the project was too expensive.

Careful: the German 'Argument' (argument) is only the factual reason in a discussion. An emotional argument or dispute is 'der Streit' in German. When two people in English 'have an argument', they are arguing; in German, they are only exchanging viewpoints.
In der Debatte brachte jeder Politiker seine eigenen Argumente vor.
In the debate, each politician put forward their own arguments.
To express which position an argument supports, the prepositions 'für' (for) and 'gegen' (against) are used. Both prepositions are followed by the accusative.
Es gibt viele Argumente für diese Entscheidung.
There are many arguments for this decision.
In a discussion, you can 'vorbringen' (put forward), 'sammeln' (collect), 'austauschen' (exchange), or 'entkräften' (refute) arguments. If you have no reasons left, you 'run out' of arguments: 'die Argumente gehen einem aus'.
Die Opposition versuchte, die Argumente der Regierung zu entkräften.
The opposition tried to refute the government's arguments.
In computer science and mathematics, 'Argument' (argument) has a special, technical meaning. You can recognize this use when the context is about functions, programs, or mathematical formulas.
Die Funktion benötigt drei Argumente, um korrekt zu laufen.
The function needs three arguments to run correctly.
reason / ground
'der Grund' and 'das Argument' can both be a justification for something. 'der Grund' is broader: it can be a cause, an occasion, or a personal explanation. 'das Argument' is used mainly when someone wants to support an opinion or convince others. That is why 'Argument' fits especially well in discussions, texts, or conversations about pros and cons. The words can be confused because an argument is often also a reason. But not every reason is an argument: rain is a reason to stay at home, but normally not an argument in a discussion.

In der Diskussion brachte er ein starkes Argument für den neuen Plan.
In the discussion, he gave a strong argument for the new plan.
Mina hat den wahren Grund für ihre Absage erst später erklärt.
Mina only explained the real reason for her cancellation later.