Many people, furthermore, believe that you cannot prove that there is life after death, but that you can only believe it by faith. There is a sort of argument present here that we can look at. People believe by faith that there is life after death. Therefore, you can only know there is life after death by faith. Filling in the basic assumption, the argument will look like this.
People believe by faith that there is life after death.
Therefore, you can only know there is life after death by faith. This general statement is simply false. This general statement is false too. But if I undertook the right sorts of activities, then I could come to know these things. This has a better chance of making some sense.