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.
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.
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.
The implications of these considerations justify the statement that all empirically verifiable knowledge even the commonsense knowledge of everyday life – involves implicitly, if not explicitly, systematic theory in this sense.
It is that of increasing knowledge of empirical fact, intimately combined with changing interpretations of this body of fact – hence changing general statements about it – and, not least, a changing a structure of the theoretical system.
Spencer’s god was Evolution, sometimes also called Progress.
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.
Among those who are satisfactory in this respect it is desirable to have represented as great a diversity of intellectual tradition, social milieu and personal character as possible.
That is, a system starts with a group of interrelated propositions which involve reference to empirical observations within the logical framework of the propositions in question.