Why is modus ponens in prepositional logic considered a valid form?
I can think of an example where a true premise leads to a false conclusion:
If the kid is wet in the winter, then it was raining on him The kid is wet in the winter Conclusion: it was raining on him
Where, in fact,
The kid is wet in the winter A passing car splashed water on him Therefore, it is not the case that it was raining on him.