EPA Foundation から抜粋ですが:
Many essay titles require you to examine both sides of a situation and to conclude by saying which side you favour. These are known as discussion or argument or for and against essays. In this sense, the academic meaning of the word discuss is similar to its everyday meaning, of two people talking about a topic from different sides. For a discussion essay, a balanced view is normally essential. This makes discussion essays distinct from persuasion essays, for which only one side of the argument is given.
１つのpoint of viewをargueするPersuasion essay と違って、discussion essay は２つ。
その２つはnormally essential と書いてますので、上記の定義では通常は２つが必要ですね。
確かにdiscussion なのに、１つしかない？となると、discussion じゃなくなってしまいます。
リンク: http://www.eapfoundation.com/writing/essays/discussion/
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