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Colleagues: 
 
I hesitated to answer this question because I thought the answer easily 
available to all.  When I looked for the definition of "industry" in 
Marshall, however, I could not find a listing in the index [eighth edition] 
nor in the table of contents.  (My eyes are not what they were, so I may 
have missed it.) 
 
Of course my answer includes the statement, "Define it however you find it 
useful to do so, but make your definition clear from the start". 
 
I habitually define an industry as a group of firms producing a product.  I 
find this justified in the first paragraph of Chapter X in Marshall.  The 
chapter is about "specialized industries" in particular localities.  So, 
perhaps my definition contains only "specialized industries". 
 
In paragraph two, however, Marshall writes of "localized industries".  Here 
industries is plural, and the conditions for the localization of these 
different industries (which I still presume to be groups of firms producing 
the same product) are those that the questioner is considering.  Perhaps 
what's wanted is a definition of "localized industries" -- I would say 
"industrial clusters" or, in an  
obsolescent terminology, "industrial galaxies". 
 
My definition leaves aside the definition of a product.  I would use some 
degree of cross-price elasticity to construct something that would be 
"operationally viable". The industrial categories in the national accounts 
use very broad definitions of "products". These definitions are very 
useful, indicating the "industrial structure" of an economy.  That, 
however, is a matter for macro economics, perhaps, or, more certainly, 
development economics and economic history.  The definition I find in 
Marshal is  
appropriate for micro economics. 
   
Robin Neill 
 
 
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