P
 
U
 
B
 
L
 
I
 
C
 

 
P
 
R
 
E
 
S
 
E
 
N
 
T
 
A
 
T
 
I
 
O
 
N
 
S
 



The 1960s to early 1980s were an era of careful specification,
complicated model building, sophisticated testing, reinterpretation and tentative resolution.
Many plausible explanations were proposed.