SCIENCE (and common SENSE ) 35 



only those of the myriad data of experience that show, through re- 

 currence, at least some minimum degree of sameness. One notable 

 exception: if attested by concordant results of independent observ- 

 ers, a unique event may be accepted as subject matter when it seems 

 to violate a supposedly inviolate system of classification. It does not 

 destroy the classification, but it shocks us into attentiveness. The 

 blazing-up of a nova, unmistakably in the sphere of the stars, stirred 

 the interest of men who had assumed the absolute changelessness of 

 that sphere. Aside from such rare exceptions, however, the criterion 

 of recurrence— minimal as it is— is one we seek to enforce absolutely. 

 Common sense rejects data rather lightly. Science does so more 

 reluctantly, and only provisionally, for science is precisely the quest 

 for "sameness" where common sense despairs of finding it. Born 

 writes that the reality of the natural philosopher or scientist 



. . . presupposes that our sense impressions are not a permanent 

 hallucination, but the indications of, or signals from, an external 

 world which exists independently of us. Although these signals 

 change and move in a most bewildering way, we are aware of objects 

 with invariant properties. The set of these invariants of our sense im- 

 pressions is the physical reality which our mind constructs in a per- 

 fectly unconscious way. This chair here looks different with each 

 movement of my head, each twinkle of my eye, yet I perceive it as the 

 same chair. Science is nothing else than the endeavor to construct 

 these invariants where they are not obvious. 



Weizsacker strikes a harmonic of the same note when he writes : 



Certainly experimental science would be impossible if nothing could 

 be perceived, but it would be unnecessary if everything could be 

 perceived. 



Now at last we can see the full scope of the criterion for selection 

 of subject matter that arises from our acceptance of the principle of 

 continuity. The unique is rejected, as intractable; the identical is 

 also rejected, as uninteresting. My writing table was here last week, 

 is here today, and I assume I will find it here tomorrow. I can 

 scarcely call this a prediction: identity is the norm I take for granted. 

 And as a norm identity is without interest. For the Greeks "phe- 

 nomena" v/ere not simply appearances but appearances of change; 

 for us, too, phenomena are divergences from the perfect continuity 

 of identity. Whether we work in science or in common sense, what 



