Should I say "competition between companies" or "competition among companies"? They're competing with each other, severally and individually. At least, that's what I think. Or is "among" justified on the grounds that competition implies vague, intricate relationships? Are there right and wrong answers in this case? The phrase is "competition between/among companies is intensifying."
The "rule" that governs their usage has nothing to do with intricacies. It's 'between' for two, 'among' for more than two. Many grammarians think the rule has outlived its use. When I'm thinking, I still differentiate.
victoShould I say "competition between companies" or "competition among companies"?
I can't see any objection to either one. Personally, I'd probably say 'between'.

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It is, I think, not quite that simple.

See http://grammar.quickanddirtytips.com/between-versus-among.aspx

for excellent explanation.
 CalifJim's reply was promoted to an answer.
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Here is a good exercise on "between vs among" from corpus sentences, so real life language: https://englishtips.com/exercise/vocabulary/8eca0782f70dc033b743ab5e7334f8dc/83 #