Various IQ tests have shown the connection between recognising valid inferences (arguments) and the level of ones intelligence; our aim here is to observe what people consider as "valid inference".
A valid argument is said to be impossible for its premise(s) to be true and its conclusion false.
A valid argument is free of counterexamples, that is, it is impossible to find a situation in which the premise(s) of the argument are true and the conclusion is false.
For example:
a valid inference (argument):
⁃ 1) Messi is in Germany therefore (=>) Messi is in Germany
an invalid inference (argument):
⁃ 2) It is snowing in Frankfurt therefore (=>) The airport in Frankfurt is closed
Inference 1 is a valid argument because there is no situation when the premise (Messi is in Germany) is true and the conclusion (Messi is in Germany) is false
However, inference 2 is an invalid argument because the premise (It is snowing in Frankfurt therefore) could be true and the conclusion (The airport in Frankfurt is closed) false.