On Error

Error is in sensation and only in sensation. All error proceeds from ignorance (and from haste).

For suppose a reasoning from something. This reasoning, suppose, is false. Another reasoning is true. What is the difference between these two acts of reasoning? What is wrong? Is it the reasoning, the mechanism thereof ? Obviously not, for since one reasoning is true and another is false, and more, since the mechanism of reasoning cannot be different in one case and in the other, error cannot be in reasoning. It must therefore be in sensation, that is to say, in the way of interpreting a fact by sensation. It follows from this that if we could be absolutely certain that our sensation corresponds to the reality, we could not reason falsely nor fall into error.

(On Error. A commentary on the Theetetus of Plato).

How do you notice error? How do you correct it? How can we tell what is reality?