If both these firms are producing bottled water and it's identical, then the goods themselves are substitutes.

如果两家公司生产同质的瓶装水,那么它们的产品是可以互相替代的

耶鲁公开课 - 博弈论课程节选

And my guess is that if we did taste tests with all you guys of all the popular bottled waters, very few people could probably pick out Evian from any other water.

我猜如果让你们,喝各种瓶装水让你们去分辨,没有几个人能尝出依云和其它水的区别

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

You could think of these as two companies producing bottled water and now we're going to get hundreds of letters saying not all bottled waters are the same, especially from Italians and the French, but never mind. Let's just pretend that they are.

把他们想象成两家瓶装水厂商吧,我估计我们会收到数百封信件,告诉我说不是所有瓶装水都是一样的,尤其是从意大利和法国寄过来的那些,无所谓了,就把它们想象成是同质的吧

耶鲁公开课 - 博弈论课程节选