In this chapter we have seen one way to respond to an extreme skeptic. That way is to deny that we need to have knowledge of objects outside our own experience and to insist that we can make do with just the experiences themselves. The effort to base all our knowledge on actual experiences is known as phenomenalism, or empirical idealism. Many people do not accept phenomenalism, though their reasons for rejecting it are sometimes strange. But we have also seen that a phenomenalist does face two problems. One is the problem of distinguishing necessary truths from contingent truths. It is not evident how experiences alone can provide such a distinction. The other is the problem of making sense of experiences, or sense data, as objects. It is not obvious when two experiences should count as the same experience, or whether the same experience can pop up at different times, and these are basic questions that should be answerable about any object said to be real.