What is a deductive argument, and what does "validity" mean for one?

A deductive argument aims to prove its conclusion with strict, inescapable logic; it is valid when the conclusion follows necessarily from the premises.

Deductive arguments try to establish their conclusions with strict, unavoidable logic. The key property is validity (Gültigkeit/Validität):

• the conclusion follows necessarily from the premises, and
• the premises provide logically conclusive grounds for the conclusion's truth.

The textbook example is modus ponens:

• (P1) All humans are mortal.
• (P2) Trudi is a human.
• (K) Therefore Trudi is mortal.

If you accept both premises, you cannot coherently deny the conclusion — that's what "necessarily follows" means.

Tip: Validity is about the form/structure of the inference, not yet about whether the premises are actually true. That distinction is exactly what the validity-vs-soundness contrast nails down.