Two normal observers viewing the same object from the same place under the same physical circumstances do not necessarily have identical visual exper… - Alan Chalmers

The experienced and skilled observer does not have perceptual experiences identical to those of the untrained novice when the two confront the same situation.

Empiricism and positivism share the common view that scientific knowledge should in some way be derived from the facts arrived at by observation.

No matter which comes first, the facts or the theory, the question to be addressed is the extent to which the theory is borne out by the facts. The strongest possible claim would be that the theory can be logically derived from the facts. That is, given the facts, the theory can be proven as a consequence of them. This strong claim cannot be substantiated.