It seems this political season fact checkers have come to the fore and everyone is busy looking into the details of what candidates say. This is good but for one point. Who will check the fact checkers to make sure they are doing their jobs correctly? It is easy for a fact checker to slip opinion into data being vetted, even if the checker is rigorous about the work. Facts are slippery. One person’s body of facts are another’s set of lies. One has to abstract himself from the noise and judge as objectively as possible what the truth of the matter is. There are obvious errors such as claiming President Obama was the founder of ISIS. There are subtle mistakes such as forecasting what the GDP might be under one’s fiscal plan. It is with these latter kinds of errors that a fact checker can go wrong. Fact checking on the whole is good. The media should be doing much more of it but with caution.