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.

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.

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

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 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.

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.

A scientifically unimportant discovery is one which, however true and however interesting for other reasons, has no consequences for a system of theory with which scientists in that field are concerned.