If observed facts of undoubted accuracy will not fit any of the alternatives it leaves open, the system itself is in need of reconstruction.

Empirical interest will be in the facts so far as they are relevant to the solution of these problems.

But the fact a person denies that he is theorising is no reason for taking him at his word and failing to investigate what implicit theory is involved in his statements.

Spencers god was Evolution, sometimes also called Progress.

But the scientific importance of a change in knowledge of fact consists precisely in j its having consequences for a system of theory.

It is probably safe to say that all the changes of factual knowledge which have led to the relativity theory, resulting in a very great theoretical development, are completely trivial from any point of view except their relevance to the structure of a theoretical system.

A theoretical system does not merely state facts which have been observed and that logically deducible relations to other facts which have also been observed.