THE PRINCIPLES OF SCIENCE 193 



Superposition and explanation. The emergence of new qualities 

 demands context{s) of interaction: certainly the interactions of one 

 or more "entities" with an environment, and usually also the inter- 

 actions of multiple entities ( like or different in kind ) with each other. 

 A gas molecule has mass and motion, but no "springiness." A large 

 number of such molecules in a particular context {e.g., a closed cylin- 

 der with movable piston) do manifest that behavior described by 

 Boyle as "the spring of the air." And now, however clearly we may 

 formerly have grasped the denotation of "gas pressure," so conceived 

 emergent from molecular impact "gas pressure" acquires for the first 

 time an explanation. Here, to a first approximation, the "outer" (en- 

 vironmental) context provides the only interaction required for 

 emergence of a new "quality" from molecules present in bulk. Con- 

 sider, however, another case. Water is "wet," we say, but there is no 

 wetness to a water molecule. The emergence of wetness demands the 

 presence of many water molecules in an "outer" context providing, at 

 least, the conditions of temperature and pressure in which water is 

 liquid, as well as any other circumstances required for the manifesta- 

 tion of wetness ( we observe no wetness if all surfaces in contact with 

 the water are waxed, for instance). But now we must consider also 

 the "inner" context of interaction among water molecules present in 

 bulk. Wetness indeed depends on the dominance of one interaction 

 over the other, i.e., the attraction of water molecule and test-surface 

 molecule outweighing the attraction of water molecule for others 

 of its kind. Wetness thus at last emerges from a double context of 

 electric interactions not meaningfully "wet" or "dry." 



The qualities of the Sahara may be supposed "emergent" from the 

 interactions, with the environment and with each other, of an im- 

 mense multitude of grains of sand. The individual grain has no dunes 

 —the quality of being duned develops from the presence of an outer 

 context {e.g., winds) and an inner context {e.g., rolling friction be- 

 tween grains of sand ) . Dunes are so e^tplained— and I do not venture 

 beyond that to the much more ambitious contention of Sherlock 

 Holmes: 



From a drop of water a logician could infer the possibility of an At- 

 lantic or a Niagara without having seen or heard of one or the other. 



This Watson at least held "ineffable twaddle," and perhaps it is. 

 Holmes' claim is one I neither affirm nor deny: I hold it completely 



