American theologian, author, and pastor R. C. Sproul reduced the problem of skeptics to four ways in which they mishandle fallacies and slip in their thinking.
1.) Contradictions – Skeptics will ultimately live with contradictions of some type. For example, some want truth yet deny truth. Some want morality yet rebel against it. Some accuse others of a fallacy, but they are guilty of that exact fallacy. Some accuse others of lying, but they twist other people’s words and lie. Some accuse others of being hypocritical, but they are hypocritical, etc.
2.) Causality – A surprising number of skeptics actually deny cause and effect. The law of causality is the first premise in the Kalam Cosmological Argument, which some skeptics are quick to deny. Some will try to oppose causality with a quantum leap (pun intended). Some try to oppose causality by exalting doubt.
3.) Reliability of Sense Perception – Skeptics often mishandle the human being’s ability to discover truth. We can directly use our senses (seeing, hearing, touching, smelling, tasting) to discover truth in reality, but skeptics often fall back on exalting doubt or they draw the wrong conclusions. On the other hand, skeptics can also mishandle the limitations of human sense perception and misunderstand universal phenomenon.
4.) Mishandling Analogies – Some skeptics are eager to tear apart a particular analogy instead of using the analogy to understand something. Analogies can help human beings understand how two things are alike, but skeptics often zone in on how the two things differ. As a result, some skeptics end up rejecting terms, truthful propositions, and higher levels of thinking if they fail to properly understand analogies.
R. C. Sproul, Defending Your Faith: An Introduction to Apologetics (Wheaton, Illinois: Crossway Books, 2003).