The Skeptics

Perhaps the oldest classification of freethinker is that of the skeptics. (The ancient Greek term skeptikos simply meant "to inquire, to examine, to consider.") 

Skeptics are those who question, who doubt, who challenge the claims of factuality in accepted beliefs and faith statements. When you make an assertion of truth, you can depend on any skeptics in your audience to seek clarity in definition, consistency in logic, and adequacy of evidence for whatever it is you say. 

In ancient times a skeptic would be willing to examine any assertion of truth, but modern skeptics are not systematic in the ancient sense (of Pyrrho of Greece) because they trust scientific research and action based on research findings. They will disbelieve what science has demonstrated to be false, and they will suspend judgment concerning whatever has not been checked. 

One can perhaps best characterize present-day skepticism as "methodological." Today’s skeptics insist that claims of factuality, both religious and nonreligious, must be tested by reason employing the rules of logic, and by the best tools of scientific investigation. They will believe, at least temporarily, whatever has passed the requisite tests, and they will willingly give up whatever beliefs prove groundless.

Agnostics