Suppose I were to stand before you today and hold up this object (in this case, a piece of chewing gum) and tell you that it is a piece of gum.
-How would you know that what I am saying is true? You could assume that I am telling the truth because you know that I am generally truthful.
-You could observe that, as I open the wrapper, the contents appear to hold a piece of gum.
-If you were close enough, you could smell the gum.
-If I had enough pieces of gum or you didn¡¦t mind sharing, we could all taste the gum to see that it was indeed gum.
-The point is that, beyond my statement that this is a piece of gum, you would have to either take my word or test the evidence in order to know for certain what is true.