218 THE ANATOMY OF SCIENCE 



sand million at the earth's surface. The errors 

 caused by the assumption of the postulate of 

 determinism may also be relatively small, but to 

 ignore them and the phenomenon of free will 

 would be like ignoring the existence of gravita- 

 tion. The prisoner cannot escape from his cell 

 through will power alone, and while the chemist 

 may juggle his protons and electrons to make 

 new compounds and perhaps new elements, yet 

 he sees no way at present of increasing or dimin- 

 ishing their number. So on the mental and 

 moral side we are limited to an extent that we 

 do not always realize. Still these limitations of 

 freedom need not blind us to the existence of 

 that power of choice that characterizes living 

 creatures, and has only been discovered in ani- 

 mate nature. 



Let us not be confused by the double sense in 

 which we use words Kke "physics" and "biol- 

 ogy." We may well suspect that the subject 

 matter of physics and the subject matter of 

 biology constitute a single continuum, but the 

 sciences of physics and biology comprise sets 

 of man-made postulates and laws which no more 

 need to be compatible with one another than do 

 the geometries of Euclid and Lobachevski. The 

 science of physics rests upon the postulate of 



