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.

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.

Theory not only formulates what we know but also tells us what we want to know, that is, the questions to which an answer is needed.

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.

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.

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

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.

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.

A gloss is a total system of perception and language.

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

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

Spencer's god was Evolution, sometimes also called Progress.

The importance of certain problems concerning the facts will be inherent in the structure of the system.

The part an actor played on stage was once written on a separate roll of paper.

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.

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.

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.