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.
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.
From all this it follows what the general character of the problem of the development of a body of scientific knowledge is, in so far as it depends on elements internal to science itself.
If there are four equations and only three variables, and no one of the equations is derivable from the others by algebraic manipulation then there is another variable missing.
In so far as such a theory is empirically correct it will also tell us what empirical facts it should be possible to observe in a given set of circumstances.
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.
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.
Now obviously the propositions of the system have reference to matters of empirical fact; if they did not, they could have no claim to be called scientific.
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.
Special emphasis should be laid on this intimate interrelation of general statements about empirical fact with the logical elements and structure of theoretical systems.
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 conception that, instead of this, contemporary society is at or near a turning point is very prominent in the views of a school of social scientists who, though they are still comparatively few, are getting more and more of a hearing.
The functions of the family in a highly differentiated society are not to be interpreted as functions directly on behalf of the society, but on behalf of personality.
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.
