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.
The main concern of the study is with the outline of a theoretical system. Its minor variations from writer to writer are not a matter of concern to this analysis.
But the scientific importance of a change in knowledge of fact consists precisely in j its having consequences for a system of theory.
The hypothesis may be put forward, to be tested by the s subsequent investigation, that this development has been in large part a matter of the reciprocal interaction of new factual insights and knowledge on the one hand with changes in the theoretical system on the other.
Special emphasis should be laid on this intimate interrelation of general statements about empirical fact with the logical elements and structure of theoretical systems.
Of course there may well be particular reasons why Spencer rather than others is dead, as there were also particular reasons why he rather than others made such a stir.