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.
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.
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.
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.
The system becomes logically closed when each of the logical implications which can be derived from any one proposition within the system finds its statement in another proposition in the same 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.
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.
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.
Thus, in general, in the first instance, the direction of interest in empirical fact will be canalised by the logical structure of the theoretical system.
Moreover, the structure of a theoretical system tells us what alternatives are open in the possible answers to a given question.
Knowledge is held to be an entirely quantitative affair. The one important thing is to have observed what had not been observed before.
The simplest way to see the meaning of the concept of a closed, system in this sense is to consider the example of a system of simultaneous equations.