The kinds of interplay between wheel, bicycle, and airplane 
are startling to those who have never thought about them. 
Scholars tend to work on the archeological assumption that 
things need to be studied in isolation. This is the habit of 
specialism that quite naturally derives from typographic 
culture. When a scholar like Lynn White ventures to make some 
interrelations, even in his own area of special historical study, 
he causes a good deal of unhappiness among his merely 
specialist colleagues. In his Medieval Technology and Social  
Change  he explains how the feudal system was a social 
extension of the stirrup. The stirrup first appeared in the West 
in the eighth century A.D., having been introduced from the 
East. With the stirrup came mounted shock combat that called 
into existence a new social class. The European cavalier class 
had already existed to be armed, but to mount a knight in full 
armor required the combined resources of ten or more peasant