From M.A. (2.4.04):

In answer to your question as to “whether there is an economic term to express the mutually beneficial relationship between supposedly unrelated manufacturing industries, such as sweet-makers and toothpaste-makers?” the answer is ‘yes’. This type of relationship which you describe is one in which one party functions as a positive externality to the other. I’m not sure that there’s mutual benefit in your example though, because how are sweet-makers benefited by the presence of toothpaste-makers in the market? Obviously it works the other way round: your teeth are rotting from the all those Opal Fruits you ate, creating a demand for the toothpaste, all this without Colgate Palmolive having to spend a penny of their marketing budget. But the other way around, I’m not too sure about…

Anyhoo. It’s like if I had a lovely garden (I don’t because I live in Brixton, so I have crack addicts and burning bins at the front of my house, but if I did) then my neighbors would benefit from it too: it would make the street a whole bunch nicer and probably jack up the value of their house a bit. However, they wouldn’t have to tend my flowerbeds. Or kebab shops, for whom nightclubs, pubs and bars are positive externalities; filling the streets with the pissed, the lairy and the hungry.

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