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The original question was about definitions other than product 
substitutability. Common usage (and hence official statistics) often refers 
to elements of joint production or at least commonality of materials, 
skills, technology, etc. Thus the oil industry produces outputs that are 
not substitutes in use (lubricants, fuels, chemical feedstocks), but are 
all produced by refining crude oil. Again, a company that already produces 
motor vehicles is better placed to produce other motor vehicles than a 
pharmaceutical or a textile business, hence the 'motor industry'. I don't 
have any references to the history of this approach, though it seems too 
well entrenched in everyday usage to need them. 
 
Tony Brewer  
 
 
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