SCIENCE (and common SENSE ) 51 



anywhere until we structure the percepts with some further concepts. 

 Though the lever's law be a "law of nature," yet we must contrive 

 to grasp it— contrive with tools mental as well as physical. Though 

 simple, the physical equipment is of considerable artificiality; the 

 concepts we need, though also simple, are substantial abstractions. 



The first of these concepts is "distance." Speaking of the "distance" 

 between F and the point of suspension of an object, we focus atten- 

 tion on what is, for our purposes, the best characterization of the 

 separation of F and object. "Distance" we hold to be independent of 

 the material composition and surface characteristics of the bar along 

 which it is measured. This kind of independence is not a priori ob- 

 vious: if concerned with the distance of a place to which we wish 

 to journey, we do consider the nature of the intervening terrain 

 (swamps, mountains, rivers, etc.). Indeed, this kind of distance may 

 be more meaningfully expressed in the Indian "moons" (a primitive 

 unit of space-time?) than in miles or kilometers. But let us suppose 

 ourselves fortunate enough to conceive "distance" as a "length" meas- 

 ured along the beam with a meter stick (or a straight spear gradu- 

 ated in arbitrary but equal intervals, and carefully preserved under 

 goatskin in an atmosphere of constant humidity within a vault at the 

 back of our cave ) . 



"Distance" singles out one aspect of a complex experience; the 

 concept "weight" demands an abstraction at least as difficult. Saying 

 "weighty objects" we come to consider one particular aspect of our 

 experience of objects that may be simple or complex, fluid or solid; 

 completely different in geometric form, material composition, and so 

 on. We so initiate a dissociation of the physical object: from "mov- 

 ing bodies" Galileo passes on to "motion"; from "weighty objects" we 

 pass on to "weight." The "weight" of a body we may conceive as 

 corresponding to the muscle pull we exert to lift it. But this corre- 

 spondence is not uncomplicated: we must, for instance, discriminate 

 the effort of lifting from the mere awkwardness of lifting a body of 

 unfelicitous bulk or shape. ( Was the difficulty of this discrimination 

 responsible for what was once the accepted opinion— that a corpse 

 weighs more than the pliant living body it was?) Fortunately our 

 appreciation of weightiness can be sharpened as we recognize one 

 obvious special case of the law of the lever. Suspending objects at 

 equal distances from the support F, suppose we choose two objects 

 that bring the system into balance when so suspended. The two ob- 



