Since StackExchange is about asking and answering questions, I came up with this problem : what is the criterion of a valid answer ?
I suppose it is a matter of the type of question you are asking, i.e what type of answer you are looking for.
For example : if you want to know the population of Kenya, you’re looking for something, that I would call a “situation”, and the answer would be the description of this situation. Answering to even such questions might be not as trivial as it seems. There are many ways to describe a given “situation” : is there a good reason to say that “52,1 M people live currently in Kenya” is a better answer than “population of Kenya is 0,67% of the world population” ? Obviously, there isn’t such a thing as a “perfect match”, what makes an answer better than an another is a matter of subjective appreciation; but both answers seem to share a characteristic which makes them “valid answers”. What is this criterion ?
Also, some questions are enounced in such a way that I cannot even figure out what would be a good answer to them. What could be, for example, the criterion of a valid answer to the question “is the world logical ?”, in your opinion ?