This argument is logically valid. But its premises are not always true. The first premise can be false – someone could have hosed down the streets, a street cleaner could have passed, the local river could have flooded, and so on. A simple logical analysis will not reveal the error in this argument, since that analysis assumes that all the argument's premises are true. For this reason, an argument based on false premises can be much more difficult to refute, or even discuss, than one featuring a normal logical error, as the truth of its premises must be established to the satisfaction of all parties.