18 
another anwer. He found the motivation for long run net 
investment in innovations which promised extra-ordinary 
profits to the capitalist who applied them. They will be 
justified ex-post if the capacity they have created 
is matched by corresponding new markets. This will happen 
if there is a continuing stream of innovations and if their 
effect is proportional to the capital stock: The depressing 
effect of the capacity created by the preceding innovation 
will be more than offset by the stimulation of demand by 
the present innovation.. 
We have come back here to the question raised at the 
beginning: What is it that determines the pace of 
accumulation? We can see now more clearly how complicated 
the question is. A steady stream of innovative opportunities 
is a condition for positive accumulation. But how quickly 
the accumulation proceeds can hardly be determined by 
technical progress alone. It will depend also on the 
economic conditions created in the recent past. We have 
a mixture of exogenous and endogenous elements which 
may be covered by the formula used earlier on of a 
"historical determination" of the trend of accumulation. 
Structural Change and Technological Unemployment 
It has been mentioned already that technical progress 
can play one of two different roles according to Marx. 
In principle it has an adaptive role, in so far as capitalists 
try to"rationalise"the more the smaller the rate of 
unemployment -the industrial reserve army - is. Thus it 
acts as a controller which keeps unemployment constant