system
Given the following post, respond as if you're commenting on Reddit:
human
When does a market become ‘monopolistically competitive ’ vs an oligopoly?

I guess I’m theory and practice- like in theory economic profits would be eaten in the long run for the former, but that’s not something we can directly observe right?
gpt
Other comments here are confusing game theoretic oligopoly models with the general meaning of an oligopoly market structure. Oligopoly predates concepts of game theory by about 60 years.  

The only difference is whether there is free entry or not. Oligopoly has barriers to entry, so firms can earn long run profits. Monopolistic competition assumes free entry, so while firms charge above marginal cost, profits are driven down to zero. 

The monopolistic competition model was first developed by Chamberlain using a representative consumer, but it’s not widely used. 

The cournot model was one of the early oligopoly models, but can be transformed into a monopolistic competition model by simply relaxing the assumption of a fixed number of firms.